Thats ironic, you have a "LEGIT" version of Enterprise, but if you update it, you get a "non genuine" message...so you don't have a legit copy, you don't have a legit version, you have a fake/keygenerated productkey and thats that. You have not got this version in the store, and you have not paid for it. So don't call it a legit version.
Yeah, sounds strange..you should report that issue to Microsoft. Shall I do it for you? As legit owner you have payed for it and now you are non genuine.... btw: Why not a simple reinstall?