You installed SIMBL, a tool for patching applications at runtime. Mac OS X isn't happy that SIMBL doesn't declare whether its event handlers are thread-safe.
You can find an explanation for this issue here:
This is a dopey cosmetic issue -- the warning is 100% spurious.
The event handler used in Snow Leopard is correctly labeled as thread-unsafe. The problem is that this warning
is about the event used for Leopard - which is completely unaware of thread issues. I can't figure out how to get
it to be backward compatible and stop complaining, so I'll let it complain.
Based on my understanding of the source code, you can try editing the
Info.plist in the SIMBL bundle and remove the following from it:
It's the Leopard-specific event handler (