Try with a clean, different IP on an incognito browser session. I noticed that once it was a kinda legit error, you know, the likes of a 404 due to their scaling issues and shit...
Nowadays each time I get the error, I switch IP and the problem 90% of the time disappears. Therefore I see 2 possibilities here. They spanned their login servers across multiple geo-specific locations that would make perfect sense, so a node in Tulsa might get busy while one in, let's say Oakland might be good to authenticate you...
The other possibilty is that this is their weak attempt to put in place a "ghosting" mechanism by returning a disguised message each time a flagged IP attempts logging in...
Whatever it is, if you're banned twitter should be clearly saying so. Just try with a new IP with no twitter cookies and see if it helps.