Thank you for your post.
Try accessing one of the files manually by typing into the Network File Path of Open Remote:
If this works, then perhaps you have a bad server.pem file. On your Windows XP machine, copy the server.pem file (found in the FileMaker Pro 11 folder) to the same location on your Windows 7 computer. Launch FileMaker Pro 11 on the Windows 7 machine and try Open Remote again.
Please keep me updated with any progress.
Thanks for your comment. I had tried this to no avail. I ended up removing FMP11 from the machines and resinstalling from a different disc. Everything works fine after this, so maybe I had a bad disc.