Out on a limb: What they may actually be seeing is a problem between their OS and .mobileprovision file which throws an error referring to entitlements. Are they seeing an error about the entitlements file when they try to sync the app with the phone?
I have seen this recently and am not fully sure of the answer. I think that on some Macs (i m thinking 10.5) iTunes is not associated with the .mobileprovision file. I have seen this twice now. The first time the answer was to have the person do an "Open With" on the .mobileprovison file and choose "Other" and then select iTunes. That did the trick.
I have been unable to find an answer to this latest event from tonight. However this person has 10.5 and also XCODE.
I m still working on this but if you have not found an answer yet, maybe the "Open With" might help.
Good luck.
Update:
I just now go the second issue solved. Email can corrupt the .mobileprovision file. I finally zipped the .mobileprovision file and sent it to those having trouble and it solved the 2nd version of the issue!