FMP 5.5 opens all files that are in a specific folder in a specific folder. Make sure all your files are in that folder. I forget the names/locations, but you should find a folder of the same name on the new server where you are supposed to put all the fmp files.
If you moved the entire folder, did you end up with an extra folder level? (Is there a folder inside a folder that wasn't there on the original server?)
Also, make sure that the FMP server service has been started.
PS. We just finished replacing our installs of FMS 5.5 with FMS 10 as we realized that the day was soon coming when OS upgrades would prevent FMS 5.5 and FMP 5.5 from working.