. can only respond to incoming message on windows live plus. cannot start conversation with my contact.

 i cannot directly contact  the one person who is my  contact i can see when they send message cos their name appear on bottom of screen but when i click the name at bottom or go onto live menu i can`t easily find the message but by trial and error and changing screens it come up and i then can have conversation. also if i try to start conversation and click contact even though their name appear in conversation box message does not arrive .Why? please help. I have windows XP on dell optiplex gl280 computer i did not have this problem on windows messenger but have it now i have windows live messenger plus