Re: fusion 6 - upgrade vm from win 7 32bit to win 8.1 32bit gives "This PC can't run Windows 8.1 ... processor doesn't support NX."

So, Windows 7 also believes that DEP (NX) is available.

Is DEP disabled in the Windows 7 VM?

From a command prompt, type sysdm.cpl.   Under Advanced -> Performance -> Settings, check the Data Execution Prevention settings.