problems adding a contact

I have a contact that i deleted some time back because i had not seen the
contact on for a long time,,,,then the contact IM's meone day...i try to
click on the message that is at the top of the box that says....this person
is not on your contact list...to add click here
I tried that but it didnt work..the line stayed high-lighted in blue..but it
wouldnt activate,,,then when i tried toa dd the contact manually,,it
said,,,you have recently added a contact with this address,,,,to add again
the contact must have a unqiue address or a different one from this
one,,,,,,help me out how can i re-add the contact to make it work.