Sorry, for clarity, when I wrote that the problem was within Zen Cart, I didn't mean to inply that there was a problem with Zen Cart, simply that it was Zen Cart which was unable to continue with one of it's database accesses, rather than say, a more general server problem.

Why does it happen? I can't give you a definitive answer because I only joined the Zen Cart community when v1.3 was released and so have very limited experience of the innards of 1.2.7 or ealier (just enough to have done a small number of site upgrades). However, I know that there were some structural changes, some of which will have affected the database structure and in this case it seems likely that Admin Profiles is trying to access a database table or field that exists in v1.3 but didn't (or was named differently) in v1.2.7.