I updated my client and still could connect to Usamot - so the question is, did the server update and break the Overviewer or is the client backwards compatible :D?
I think minor updates are supposed to be compatible. Not sure though. I don't know if there's any rhyme or reason in the releases.
I read that 1.2.4 and 1.2.3 are not compatible, but 1.2.5 and 1.2.4 are.