Had this happen to me and have seen some others mentioned elsewhere.   So I will add it to the list.

Saving a pz3 (or pzz) with Exteternal Binary Morph Targets turned on can lead to the pbm file becoming corrupted which will cause Poser 7 to crash and close when you attempt to (re)open the pz3.  If you delete (or move) the associated pbm file, Poser 7 will prompt it can not locate the pbm and ask to locate it.   Telling it no will allow the pz3 file to open (allowing you to salvage something of your work) but without any of the morphs (as these are stored in the corrupted pbm file).  

The Save File option (found in General Preference Tab>MiSC) External Binary Morph Targets is set on by default.   You may want to consider unchecking this box (turning it off) until this issue is addressed. 

I am not aware if also occurs with items saved to the library using pbm.  I have only experienced it (and read about it) in regard to pz3 (pzz) files.