Can't see a specific buddy

Question

I have PCs running AIM with two different screen names - let's call them screen names H and T.
My daughter has an Mac Book Pro running iChat with a screen name - let's call it screen name B.
H and T can talk to each other using either PC. B and T can talk to each other. In fact, B has a very long buddy list and can talk to lots of people. But H and B can't talk to each other. They always appear to be offline, even though T can see them both and talk to both.
We can't find any evidence of blocking, we've deleted and re-added to the buddy list, and I've searched the internet and this forum for help. But I'm stumped.
Any ideas? Thank you!

Answer 1

Well....
B must know the difference between adding AIM or @mac names - so we can rule that out.
We can presume that B has not blocked H
Blocking of B by H would produce the symptoms described.
Lets leaves Both B and H misspelling each others names (Very unlikely both would)
Possibly, one has Misspelt and then has "Only Allow People in My Buddy List" set so the other person is not accepted - Would also produce symptoms described.
One person is set to be Invisible (Less likely as T would not see H either)
B has exceeded the max Number of Buddies.
Options:
Delete/Change all Blocked Lists
Remove any setting to Allow Buddy List only
Remove extra/Spare Buddies.
Use B's Screen name on one of the PCs (Or in AIM for Mac) and see how Many Buddies are in the "Recent Buddies" group that iChat does not see and drag them out and delete others where required.
If T starts a Group chat, can they pull both the others in ?
B can then use the Buddies Menu to Add the Buddy by the Name or by Dragging to the Buddy List.
6:42 PM Sunday; September 2, 2007