Kirk,
On a Win7 64-bit system:
I just ran into the same issue that NEF files edited in NX2 or TIFF files generated in CS5 refuse to accept crops using PM5 RC. Also, using PM4.6.9 I can crop these images without problem.
Seems that in V5RC2 the cropping now works fine on all TIFF files and NEF files :-)
Also, crop marks made in PM4.6.9 are not visible in PM5 RC and vice verse.
OK, there are still compatibility issues.
Crops made in V4.6.9 to NEF files are visible in V5RC2, but cannot be changed (moved, resized) in V5RC2. They can only be removed.
Crops made in V4.6.9 to TIFF/JPEG files are visible in V5RC2, but cannot be changed (moved, resized) in V5RC2. They can only be removed.
Crops made in V5RC2 are visible in V4.6.9 unless one rotates the crop. But as soon as a TIFF or JPEG file was touched by V5RC2, cropping in V4.6.9 does not work any longer for these files (actually, it does work, but does changes are not visible in V5RC2)
So, there is still a big compatibility issue for cropping in V5 or earlier versions.
Looks like the cropping information for a file gets out of sync between the two versions and/or write to/read from different locations.