The only problems I recall from running 3.0 were with VOIP.
I still have them on 3.5 but replacing the ATA fixed them mostly, or at least remediated.
Perhaps you can mention what softs of problems you are getting and someone might pitch in with an idea.
I run ZS on various hardware for at least 10 years since v. 1.0beta3 and ran 2.0, 3.0 and now 3.5 with no show-stopper problems.