This page is designed to run through some of the most common problems you might have when trying to use the interactive modellers available on the USS website. If you are unsure why the modeller is not working, read through this page in order to try and diagnose the problem.
Java applets can be embedded into web pages to provide extended functionality. In order for a Java applet to work it is required that the user's computer has a Java Virtual Machine (JVM) installed in which the Java applet will run.
In most cases, the loading and the subsequent running of the applet is completely automatic and the Java applet simply appears as part of the requested web page. Also, in most cases, a JVM is either bundled with the user's operating system or web browsing software and is installed and enabled by default.
However, due to the wide variety of operating systems and web browsing software available and being used, some problems are inevitable. The rest of this page aims to explain and provide solutions for most of the known problems with using the modellers.
Common problems and solutions
Before trying to diagnose any modeller problem, it is recommended you do the following:
- open the form in your browser window
- with the window in focus, press CTRL+F5 (Windows users) or APPLE+R (Mac users). This will ensure the latest files for the modeller are downloaded from the webserver.
If there is a specific problem that can be identified from the list below, simply scroll down for an explanation of how the issue can be solved. Please read the problem descriptions carefully as many problems can share the same symptoms.
- "Java disabled" warning message
- request to install "Microsoft virtual machine" plug-in
- "java.lang.classnotfound" or other Java error
- security warning pop-up
- blank grey box instead of the modeller
- blank page instead of modeller.
1. "Java disabled" warning message
When accessing the modellers page you receive a warning message that Java is not enabled.
Without enabling Java the modellers cannot be run. This check cannot diagnose the exact reason why the user has Java disabled, but its purpose is to inform the user that further action is required before the modellers can be used.
Java can be disabled for several reasons. To fully diagnose the specific problem please read the 'Java Virtual Machine not installed', 'Java not enabled' and 'Custom security settings' sections on this page.
2. Java Virtual Machine (JVM) not installed
Windows 95 and some versions of Windows XP do not come with a JVM installed. Also, a JVM is not included with the Mozilla browser and custom installations of Netscape may also be installed without a JVM.
Not having a JVM installed will cause the modellers to fail:
- If you are running Internet Explorer and has "Install on Demand" enabled (which is the default option) you should receive a prompt asking whether you wish to install the "Microsoft Virtual Machine" when trying to access a modeller.
- If you are unsure whether you have 'Install on demand' enabled or a 'JVM' installed you should check in your Internet options dialog under Advanced options.
- If a JVM is installed there will be a sub section titled Microsoft VM or Java (Sun).
- If you are running Netscape or Mozilla you can check for the presence of an installed JVM by clicking Help/About Plug-ins. If "Java plug-in" is listed then the user already has a JVM installed.
Unless you are using Windows 95 they should go to http://java.sun.com/getjava/ and follow the instructions on this page to download and install Sun Java.
Microsoft and Sun no longer support Windows 95 and USS provide no guarantee that any of the modellers will work with Windows 95.
However, if you wish, it is still possible to get a JVM for Windows 95 . This can be done in two ways:
Apple Mac users
If you are a user of OS 9 for the Mac you may find that the forms preceding some of the more advanced modellers will produce unexpected results and you are unable to proceed onto the modeller screen.
In most cases the only solution will be to upgrade to Mac OS X. One point to note is that Internet Explorer versions for the Mac do not correspond with the equivalent PC versions. This means that Internet Explorer 5 for the Mac does not provide the same functionality as Internet Explorer 5 for the PC.
The missing functionality means that Internet Explorer 5 for the Mac cannot process the validation rules required for the forms preceding some of the more advanced USS modellers thus preventing access to the modeller.
There should be no problems using the modeller on Mac OS X with Internet Explorer 5.2.
The operating system OS 9 is no longer supported by Apple and USS provide no guarantee that any of the modellers will work.
3. Java errors
You may experience java.lang or other Java errors. This problem could have several causes:
- Due to the personal nature of some of the information entered into the preceding forms of some of the more advanced modellers the data is encrypted when it is sent to the web server. In order to guarantee the validity of this encryption USS has been issued with a security certificate.
- When using Sun Java it is necessary to manually accept the security certificate, by means of a dialog box, in order for the modeller to be able to communicate with the server.
- If you reject the security certificate the modeller will fail and an error may be reported in the status bar or the Java consol
- Other Java errors may be caused by corrupt or very old implementations of the JVM being installed on the client machine.
- If you are trying to access the modeller from behind a server configured with Microsoft Proxy or Microsoft ISA server software you may receive classNotFound errors when accessing a modeller using the Sun JVM. This happens when the Microsoft server is configured only to use Microsoft's own proprietary authentication protocols. The Sun JVM cannot access the internet when it is behind such a proxy server.
The solutions to these problems are outlined below:
- The security certificate induced errors can be solved simply by accepting the security certificate when requested.
- Errors caused by corrupt or out dated installations of the JVM can be corrected by downloading and installing the latest version of a JVM. Instructions on how to do this are available in the 'Java virtual machine not installed' solution above.
- There are two solutions to the problem caused by trying to use the modeller from behind a Microsoft Proxy server.
- If you are using a Windows machine you can switch to using the Microsoft JVM in your internet options under the advanced tab. Exceptions to this include some Windows 95, Windows XP and non Windows users, who do not have the Microsoft JVM installed. Windows 95 users can obtain the Microsoft JVM as outlined in the 'Java virtual machine not installed' section.
- Microsoft no longer distributes the Microsoft JVM for Windows XP. Windows XP users without the Microsoft JVM can now only install the Sun JVM. These users, and users of non Windows computers will not be able to use the modellers from behind certain configurations of the Microsoft Proxy and ISA server software. The only solution here is for the Microsoft proxy/ISA server to be reconfigured to allow standard authentication protocols (Java 1.4.x supports the RFC2617 Basic and Digest Access Authentication). This solution can only be implemented by system administrators and may not be a feasible solution on the users particular network.
4. Java not enabled
If you are using Netscape or Mozilla you may find that running a modeller brings up an empty window (some modeller windows may contain "print" and/or "back" buttons at the bottom, with a blank space above them). This happens when the JVM has been disabled in the browser's preferences.
Providing you have a JVM installed, it can be enabled in Netscape and Mozilla by opening the Edit menu then select the Preferences option. In the Advanced category there is a check box marked as Enable Java, this should be ticked.
5. Custom security settings
If the default security settings for Internet Explorer have been modified, it is possible to prevent Java applets from running. If this has happened Internet Explorer users may receive a security warning such as "Your current security settings prohibit running ActiveX controls on this page. As a result, the page may not display correctly" when trying to access a modeller. Once you have clicked "ok" the modeller does not appear. This warning can also appear if you do not have a JVM installed and has Install on demand disabled. You should read the 'Java virtual machine installed' section to make sure this is not the case.
In order to give permission for Java applets to run you need to alter your Internet Explorer security settings. To do this you must go into the Tools menu and select Internet options.
From here you need to select the Security tab then select the Internet zone and click on Custom settings. You need to scroll down the list until you come to the section labeled Microsoft VM. You will need to select High safety under Java permissions.
6. Java Runtime/virtual machine (VM) out of date
A grey box is observed where the modeller would be expected to appear. This is usually a sign that an out of date, unsupported virtual machine (sometimes referred to as the Java plugin, or Java Runtime Environment) is installed.
Please download and install the latest version of Java.
If you are using the Cost of Contributions calculator you may not have Flash installed (the software used to make the modeller work). To download Flash please click here http://www.adobe.com/support/flashplayer/downloads.html
If you are unable to diagnose and/or solve your specific problem you can request further support by emailing the webmaster.
The more information you provide about your specific problem the easier it will be to try and find a solution.
If possible, please include:
- the modeller you were trying to use
- the exact problem you have encountered
- any error messages received
- the operating system you are using e.g. Windows 95/98/ME/2000/XP, Mac OS X, UNIX etc
- the make and version number of your web browser e.g. Internet Explorer 6, Netscape 7 etc
- whether you are using the Microsoft or Sun JVM.