BEST PRACTICE: Check ALL file with high magnification BEFORE you use the file, whether it is free, a paid item, or something you built yourself. Handles sometimes get twisted around and form a loop, which will drive your system to do things you do not want it to do.
I did this for a friend on a file he used which totally tore up a board. It was a purchased item and had so many problems that it took me quite a time to correct. Once he got it back it worked as it should have.
Also, importing files can be hazardous! You don't always know for sure where the file has been built, which system it was tested on, or which processor was used during the test. Importing such a file into Aspire - you should always give the file a good once-over look to assure that you have eliminated problems before they even start.
Aspire also has a handy tool to check your vectors - listed under the Edit Objects option titled "Vector Validator".
It will list for you any problems of "Zero-length Spans", "Overlaps", and 'Intersections". Use this tool on EVERY FILE YOU ARE GOING TO USE, BEFORE YOU USE IT TO MILL.