iChat not adding buddies

[bridge1490]

When I try to add a buddy into my iChat buddy list, the buddy appears online for a few seconds and is deleted from the list. It happened every time I try to add a new buddy.

[Giaguara]

Odd.
'Show groups' - what group are you trying to add them?
What version of iChat?
Have you ever been able to add any user to your iChat account?
Do you have another iChat/AIM account to check if it's happening there too?