Hello,
I need to connect with ICQ 99b but I think it is blocked by the
servers because they want to force you to get the latest version. I
won't upgrade to any higher or lower version and want to know what I
have to change? I think I'll need to modify something in the registry
(maybe the version number or something else) or maybe in the dll's to
be abled to connect.

All versions over 99b (2000a,2000b,...) connect properly.

You are abled to get ICQ 99b (and also 2000a,2000b,... maybe for
testing purposes) from:

http://www.oldversion.com/program.php?n=icq

Thank you guys and good luck.