J2SE Version (please include all output from java -version flag):
6u15

Does this problem occur on J2SE 5.0.x or 6ux ?
works fine with 6u10 and 6u13

Operating System Configuration Information
Microsoft Windows Vista SP1 & SP2

Hardware Configuration Information
Lenovo ThinkPad and ThinkCentre


Description:

We have recently started to deploy JRE 1.6.0_15 to a number of our test Vista clients. We have immediately come across an issue where the users are 'prompted for credentials' when launching Java content. From the Java Console we get the information below

The error in the JAVA console is

load: class com.ibm.rmc.search.SearchApplet.class not found.
java.lang.ClassNotFoundException: com.ibm.rmc.search.SearchApplet.class
at sun.plugin2.applet.Applet2ClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader.loadCode(Unknown Source)
at sun.plugin2.applet.Plugin2Manager.createApplet(Unknown Source)
at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
at java.lang.Thread.run(Unknown Source) Caused by: java.io.IOException: open HTTP connection failed:http://pdm.is.astrazeneca.net/AZCustomDevelopment/com/ibm/rmc/search/SearchApplet/class.class
at sun.plugin2.applet.Applet2ClassLoader.getBytes(Unknown Source)
at sun.plugin2.applet.Applet2ClassLoader.access$000(Unknown Source)
at sun.plugin2.applet.Applet2ClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
... 7 more
Exception: java.lang.ClassNotFoundException: com.ibm.rmc.search.SearchApplet.class


On further investigation we have found that U15 seems to be ignoring our proxy routing script on our ISA 2006 configuration, if we direct the client back to ISA2000 we do not get the error. We have configured Java network settings to 'use browser settings' hence why it hits our Proxy servers and would not be able to configure 'network' to either of the other settings due to the impact on other JAVA based applications.

Here is some information from our networking support team ...

It's a client thing - the client (ie the JVM I guess) is sending the requests to the proxy whereas it should be sending them to the web server direct. It should be able to read the routing script and decide whether to send to the proxy or direct based on that. Ultimately that's the bit that isn't working.
 
It's not something we can fix on the proxy. I think the problem there is to do with authentication - when the request is proxied, the user info is lost which results in an anonymous request getting sent to the web server by the proxy. That's why the authentication dialog comes up.
 
The guys in Japan tested a couple of things
 
1 - setting the java client to use no proxy settings rather than use IE settings
2 - allowing anonymous access on the web pages java is trying to load
 
Both these worked but they're not practical.