I had the same issue a few weeks ago.
I was mass uploading pass protected files (content locker attempt) and around the 5th upload the whole thing took a shyt and was gone, I then tried to make a new account and after several attempts at the captcha, I assumed my ip was being blocked, which turned out to be true, because I couldn't even upload with my main account, captcha kept failing.
I then drove over to mcdoanlds and jumped on their wifi and problem solved.
The truckstop I was at, to this day, it refuses to accept the captcha.
interesting.