Simply convert them to DNxHD or similar. ProRes and PC is just not smart despite Apple supporting it - in theory. It's simply nothing anyone with some sense left in them would work with on a PC. This could be a million things, including compatibility issues with ProRes created by recorders like AJA Ki or GoPro cameras. Impossible to find out from a distance.
Thank you for your response.
So one issue may be the differences in writing the proRes file from different brands of recording decks - correct?
RE: the lack of "sense" for working with proRes on the PC. The idea of proRes for the PC was brought to me by a video producer I work with as a solution to codec issues we have with SonyXD Cam HD files on the PC. For AE 4 and 5 the proRes clips did work just fine. But this last shoot was done in a different city using a different brand of proRes recording deck.
So if proRes IS NOT the sensible thing for PCs, then in, your opinion, what is most universal codec, off of Sony XD Cams, that will work on PCs running CS4 - CS6?
I work on ProRes files very often in After Effects on a Windows machine. You should have the latest version of Quicktime 7 for Windows. Any machine that does NOT have Final Cut Suite 3 installed will not be able to write ProRes files, but it can read them.
I write to a different codec for Quicktime. I use the PNG codec. It is 10-bit like ProRes, bue it is also lossless and it supports alpha channels. The file sizes are very large; if this is an important consideration, you should use a different codec.
Mylenium's suggestion of DNxHD is good. It is a good method for exchanging video files between Macs and Windows machines.