i encountered the same problems with the trials
if you changed the hardware (it's already enough to change perhaps the NIC or whatelse) on which Adminstudio was run before you can't install the trial on the same machine again
(at least i needed three machines for testing porposuses)
it's seems that even the trial version does some checking and "burns" a internal checksum on the PC
(like Windows 2000/XP and newer OS'es does, so called WGA) to avoid more than one installation of AS on the same machine
i also wasn't very amused about that. But in our firm we recently bought a "real" license and the problem was gone then.