Registratioon problem
 

Hello!

We have a problem with registration. For example we have a user with "John" nickname. Any new user can register with "john" nickname. How can we solve this? I couldn't find.

I was under the impression that wasn't possible, and that case sensitivity wasn't part of the registration check. What are some of examples of the actual names being re-registered?

For example:

http://forum.azeri.net/members/67-aygun.html

http://forum.azeri.net/members/32418-aygun.html

That should not happen on a totally default vbulletin board. Try disabling your modifications/plugins and see if you still have this problem (try registering an existing username).
Note: To temporarily disable the plugin system, edit includes/config.php and add this line right under <?php

There is only VBSEO installed at our forum.

The registration code checks for an existing user name by doing a query of the database, and it uses '=' to compare the strings. '=' is normally case insensitive, but that depends on the character set/collation (which I really don't know anything about). So I'm thinking maybe your database settings for character set and/or collation is causing it not to recognize upper/lower case letters as the same. But unfortunately I don't know how you'd go about fixing that.

How can I solve this? :(

If it's something like kh99 suggests, then you might need to check with your host to see if the database is the issue.