Neither my Premiere nor my S3 can find previously recorded Tivo files on my PC. They used to w/o any problem. I used to be able to push and pull .mpg files back and forth. Now they can't locate them. Did Tivo do something nefarious?
Is the TiVo not seeing the PC at all? Or is it not listing the files when you browse the PC?
If it's not seeing the PC at all then it's likely a network or firewall issue. If it's not seeing the files then make sure that TiVo Desktop has the My TiVo Recordings folder pointing to the right drive. I've also seen situations where there is one bad file in the directory that will cause TiVo Desktop to choke and prevents it from displaying any of the files that come after that one.
Developer for VideoReDo
Found it! ggieseke had the answer in another TiVo forum thread. Running AVG as I am, you have to manually open UDP port 5353. Go here on how to do that: http://support.microsoft.com/kb/308127. Works perfectly now.