Hmm, is it the first time you see it? And if you clear your java plug-in cache, does it fix it? In another browser (before clearing the cache)?
Thanks for reporting.
I see in the stack trace:
Caused by: java.lang.OutOfMemoryError: Java heap space
What was the status of your system memory?
This is the first time I've seen it (although I don't think I've tried playing Incredibuilder since you first put it up here). Clearing the cache did not help. I have over 2GB of free completely unused RAM. Apparently I don't have Java installed on Firefox (which is BS), and Incredibuilder seems to completely take down Opera.