Hi.
SEE THE NEXT POST TO SEE THE REAL NATURE OF THE PROBLEM.
Thanks for the info. Here's my take on this problem, and what you should do about it.
It's YOUR system, so ultimately I can't tell you what to do !!

Strip off 64 bit Java, and install 32-bit Java. See if the problem comes back.
I am delighted to see you are using the Server VM. Do the same thing with the 32-bit Java.
I know we all think that 64-bit should be faster on a 64-bit chip, but actually I am told that 32-bit Java is FASTER.
All of my experience is with 32-bit Java, mostly because I have had to use 32-bit native DLL's from time to time....
Again, it's your system, and I have little experience with Java 7. I have frozen my versions at the end of the Java 6 series for a while.
I can almost guarantee you that the problem is with Java Web Start, and that the normal Java runtime does NOT have this problem.
The nature of the problem is that the Java Web Start ClassLoader permits key classes to be Garbage Collected.
This has the knock-on effect of security classes, and other such things being unavailable and/or Bogus security exceptions preventing the loading of certain classes....
HENCE the barrage of error messages relating to missing classes, etc....... SECURITY problems and "Trust Level" issues. These issues did not exist when you first started but while it was running, key security related / authentication classes are lost, and so then the authentication / "trust" security stuff fails forever, and there is no recovery.
For LONG RUNNING processes running under Java Web Start, in VM's which have this bug in Java Web Start, the only workaround I know of is to "lock down" classes so that they are NOT GC'd. These are Java Web Start entities which get "kicked out" of memory and thus cause this pathological situation. It's a Java Web Start BUG.
An example of this I have posted, which applies only to code where you are able to include the "fix" in your own startup.
If I were you, I'd nuke Java 7 and install the latest 32-bit Java 6 series update. But that's just me

So that you know this is a real problem, and that there is a workaround, I posted this workaround here:
viewtopic.php?f=65&t=48731Problem is, it may be version specific, and so I don't know how generic it is. You could only use such an approach in your own code most likely, so it might not apply to you. Really pissed me off to know that Java had problems like this internally in the Java Web Start classloader. Maybe Oracle has made things better...
HyperScalper