Close UT
Look in your user.ini (system folder) and find:

ClientKey
ClientID

Erase what is under value and start UT up again.
(eg. change Name="CilentID",Value="xxxxx" to Name="CilentID",Value="")

is it works at all? admin wont ban you? when you change that config?

actually there is no such words in user.ini file

Yes there is.

Under [NextgenCC.GeneralConfig]

right there is nothing like that

and u really mean ut user.ini

If there is no such line in your user.ini, then you probably haven't played in a server with Nextgen feature.

I do not know any servers with that by heart, but I'm sure they exist, because I've been deleting that section in User.ini over and over again.

Yep!  If they dont have it they haven't played on on.  But yeah you can delete the whole section instead haha.  I just made a simple program to delete what's in those fields for me in C#

Yeah - so did I in C++ and that's why I'm deleting whole section, because it's easier with ini features in C++. No need to edit and stuff - just delete.

Code of NexGen110 shows:
if you got no/empty ClientKey or wrong ClientID in your User.ini, you get a new ClientKey which is only a random string out of with the pattern - NexgenUtil.uc.
Further the ClientID is just the MD5 Hash of the generated ClientKey string.

This is a batch code which just strips of those two lines in the User.ini:

let me try it