When I'm at a lan-party or just anywere els but at home with my computer, and i try to connect to IRC, it says:

Your username is invalid.
Connect with your real username, in lowercase.
If your mail address were foo@bar.com, your username would be foo.
-
Closing Link: xxxxx by splatterworld3.de.quakenet.org (USER: Bad username)

but when i'm home, there is no ploblem with connecting...

Connect with your real username, in lowercase.

Sounds like your ident/username has uppercase letters in it. alt+o | connect. Then make sure the "email address" is in lowercase, then go to the Identd section and make sure "User ID" is in lowercase.

hmm... Now i have tryed all u sayd, but sadly, I had no luck... still wont connect...

do you all using the same connection? if thats the case.. can the others connect to irc? and if they cant look at the same things on there mIRC options..

That is what i dont understand... cuz the others can connect without any ploblems...

Well if other people are using the same connection, then perhaps you are getting disconnected for cloning.

your not making your ident part match your nickname ..... make it match and it will work for u

Do what the notice said to do:

Type /identd on foo then reconnect...