java.lang.error 91

[jumpjack]

Uncaught exception: java.lang.Error: 91
- java.lang.Class.invoke_verifier()
- java.lang.Class.verify()
- java.lang.Class.initialize()
- java.lang.Class.forName()
- com.symbian.midp.runtime.MIDletExecutor$MIDletConstructorThread.run()
java.lang.RuntimeException: java.lang.Error: 91
- com.symbian.midp.runtime.MIDletExecutor$MIDletConstructorThread.run()
*******************
*******************
JASSERT: ASSERTION FAILED!!: Destroyer: Non-midlet thread group not handling exception!
*********

What does this mean?!?
It comes out upon running a midlet on my Motorola a1000 UIQ device. The midlet is attempting to use FileConnection API, which appears to be supported by the phone. I have an uncertain remembering about some kind of limitations I found out existing in this implementation, but I can't remember exactly.

How can I understand from that weird error message what exactly is going on? FC API is supported but....?