Hi Mike,
Start with going to your iChat > Preferences > Accounts > Security.
Check they are Allowed if you are using Allow Specific People.
Check they are not in the Block list (iChat 4 upwards will show them as Off line but with the word "Blocked" underneath).
If they can contact you, go to the Buddies Menu and see if the Add option shows their Screen Name and is dark.
If it is most likely you have misspelled their Scree Name.
At their end get the to check their Security settings.
This can be difficult as many will think they know what they set.
Confirm that they are not set to Invisible.
Also the following applies to both ends.
If you have a second Mac User Account (I have one called Test) and have then used your main iChat details to test iChat AND Parental Controls then go back and undo any setting as it will override what you are trying to do in the security settings.
By Default Parental Controls using the iChat and Mail option Blocks all Buddies.
Adding Buddies to the Allow List then Unblocks them. Not Undoing this will leave your Buddy list as it was last Flagged by the Parental Controls.
This is further complicated but the none use of the "When iChat is Quit, Set the Status to Off-Line" option that leave you Logged in (related to Off Line IMs).
Your Buddy may think he has not Blocked you but using Parental Controls this way he may have NOT Unblocked you properly during a test.
8:09 PM Friday; May 28, 2010
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
