UPDATE:
Ok I backed up the reg entry, and then deleted the user name & password fields from reg.
Upon loading game you get the reg Date Of Birth entry etc, and then option to login to existing account or start a new one.
I tried entering existing my player user name/password (which works on-line), all I get is "
Account cannot be found"
(Clearly a massive bug as I can login from web which means if I reinstalled I would never get the game to work again).
So then I tried new account, and all I got was "
Reg key is already in use"
(showing that key is tied to account fully)** I then put reg entry back & ONLY deleted the password. When I loaded the game it loaded normally with usual 2k server error, so it proves its not logging into account or checking the password in the reg properly.
** I used a text to binary conversion tool to convert my correct password into binary string & then entered this into the reg password line, I still get server error, so it definitely looks like its online account issue than local as its not even referring to that password line.
I have come to the conclusion that once you reset the password the online account becomes not found by the game, so not only does your online my player account become unseen it also then wont revoke key locked to it.
So basicly NEVER EVER UNDER ANY CIRCUMSTANCES change your password for myplayer, its completely bugged and you will loose online features.Id advise everyone to export that reg entry even though things are ok. As soon as I exited game, re imported the reg entry, loaded game, I was back in as normal but as normal 2k server error.
What worries me is how on earth do you uninstall this game and then install to a new account if key is locked to myplayer account & added the same account info = "account not found"? I dont see how 2K have setup a process to "Revoke" your key from that account, what very poorly implemented process. I can imagine if entering existing account would not error out, password would match and I would be back online again.
Anyway nothing more than 2K can advise now as I have tickets open, seems to me the only thing that can be done is them supplying a new reg key for the sake of a password change bug, dear oh dear.
Funny thing for me is, I only reset passwrd becuase 2k site would not log me in, only to find I never needed to do it anyway as I was looking at 2k12's myplayer site not 13 ... so I pretty much killed online for the game for no real reason ...

(still 2k's bug though).