Hello, I get this window when I open lfsforum. It's the opera's JS error console, so I think something is wrong with the JS on forums. It's quite annoying when it pops out on every subpage...
Opera 10.00 Beta 2

Also Opera 10.00 Beta 2 user - no problem here. Nothing pops out.
I couldn't reproduce it, check attachment.
Win XP, latest Java. 'Exceptions Have Stacktrace' from attachment is ticked off.