Currently Being ModeratedNov 15, 2013 2:00 PM (in response to shl93)
I have an Apple ID that is a email from an Dial up service I once used.
(actually I can still download mail from this service but cannot send unless I login using Dial up)
When iCloud came out I linked this to iCloud and was given an @me.com ID as well.
Later Apple changed these to @icloud.com and I got one of those as well.
For iTunes, Logging here to post or accessing iCloud in a Browser I can use anyone of on the three "names" but with one common password.
In Messages or iChat though this Apple ID does not work.
It has to be one of the ones Issued by Apple.
Changes in iChat 6 and the two Messages version in Mountain Lion and Mavericks that use a Login to Apple as well as AIM to Verify things before AIM is allowed to "read" the Password means the later IDs issued under iCloud will not work in iChat 5 or earlier.
@mac.com names issued under the .Mac service or as "iChat Names" during the MobileMe period will still work in any version.
If you have the @me.com or @icloud.com IDs use those (even if it says @me.com on the setting in iChat)
Add the ID in full to the AIM setting option.
If you don't then Register a name at AIM.
iMac 2.5Ghz 5i 2011 (Mavericks 10.9)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad