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1.
Every program causes this in Windows.
Explorer.exe has performed an illegal operation and will be shut down immediately.
by MEarnhardtFan August 25, 2004
 
2.
If you have windows, your probably experiancing it right now.
(Illegal Operation Popsup) "Hey, wtf? I was reading about how lame Bill Gates was!" (Illegal Operation: That's why this popped up dumbass.)
by DennisTehMenace March 30, 2003