Script error in yahoo messenger..need help

Hello!!
Just want to ask a help from u guys on how can I solve the script error that pops out everytime I open the conversation with my BF..when i click the show recent message the script error is appearing...strange that it happens only with my Bf's conversation..my other contacts is okay...this is the script error line:7 charge:16553,error: 'Sender' id is null or not an object it says. my yahoo Id is the problem or my Bf's yahoo id??or any problem ???

please help me on this.....thank you so much..your help is highly appreciated...Thanks...