Problem: My browser shows the JNLP file for my application as plain text. Most likely, your Web server is not aware of the proper MIME type for JNLP files. See the Setting Up the Web Server section (page 525) for more information.
Furthermore, if you are using a proxy server, ensure that the update versions of the files are returned by updating the time stamp of the resources on the Web server such that the proxies will update their caches.
Problem: When I click on a link to a JNLP file with Internet Explorer and Java Web Start launches, I get the message "Could not load file/URL specified: C:\Documents and Settings\…\application.jnlp". This problem only occurs with Internet Explorer. It is usually caused by a no-cache directive from the Web or proxy server, which causes Internet Explorer to not write the JNLP file to the local disk.
This frequently happens when you upgrade a Tomcat-based server, as later versions set the no-cache directive by default for any resource that is within a security constraint in the web.xml file. Try removing the relevant URI from the security constraint.
This problem can also occur because of a full cache or if the cache is turned off in Internet Explorer.
Problem: My browser seems to find the JNLP file, but Java Web Start says it can't find it. The most likely cause is that your browser and Java Web Start have different proxy settings. To modify Java Web Start proxy settings:
Open the Java Application Cache Viewer.
From the Edit menu, select Preferences. The Java Control Panel opens.
Click Network Settings. The Network Settings dialog box opens.
Select Use proxy server, enter the proxy server name and port number (typically 8080).