I can open a .book file but not a .fm file with FM 10.0.2

I can open FrameMaker 10 through the EXE.

I can open FrameMaker 10 through a .book file.

I can open a .book file from FrameMaker 10.

I cannot open FrameMaker 10 through a .fm file.

I cannot open a .fm file from Framemaker 10.

I've tried multiple .fm files, so this isn't isolated to s sngle corrupted file.

I was using FrameMaker 10 yesterday, but it doesn't work today.

I updated Flash this morning, but have not installed any other programs.