Had the same program built a good part before the crash? Were there any programs loaded or verified between good parts made? Depending on the size of the end mill, it would probably have to be "driven" into the part to get it up to the collet chuck, but you said the end mill was buried in the part, so I think it wasn't small enough to just shatter, (so not just a collapse). It is an error in the code, or "O.E."
Feel free to correct me anyone.
My 2 cents, Robert
The beaten path, is exclusively for beaten men.