Hi,
I'm not aware of any workaround. The reason for it not working is (I think) that it (PM) is a 16bit application and that the 64bit versions of Windows doesn't support 16bit applications any longer. There's a note about it on Melabs site.

I've compiled and assembled code for anything from 12F to 18F with PBP2.60 and MPASM on Win7 64 bit. I'm sure someone around here will figure out the problem if you provide some details.