yahoo chat problems

Hi there ,if anyone can help me it would be great. I got pm from somoene in yahoo chat, and then a yahoo message box came up and said that that user was attempting to take files fom C:/documents so on and i clicked no that i dont wat to give access to this person,,,,and i guess he kept on tying to put the box up/ I find this very fustrating and i want to stop this from happing in the future. At times today useing chat i could not type any text into the room as well as IM's. I had to restart yahoo mess altogether. Why am i having this problem and how can i prevent it and how can i report these lousers ?? thanks a bunch.