died unexpectedly ???

It may happen for various reasons - version 9.0 and 9.1 been very buggy. One reason tough to catch is if you draw structure with no snap to vertex. I have had cases where 2 vertices differ in the 5-th or 6-th digit of their coord and mesher died...unexpectedly...Since hfss keeps log on the structure, you may like to see (it is html format) and inspect. Generally redrawing with snap enabled will cure...
If you import it is ver likely it dies too.

From my experience:
1. Problem with reading license files.
Try reinstalling the program.

2. Problem with the hard drive, if it can't read/write quickly enough.
Try using different PC.

:D