Shoutbox

I run windows messenger live 8.1 and plus 4.23
I've never previously had any problems and there doesn't seem to be anything triggering the problem. But today when i tried to access my chat logs i got this pop up:


then when i click open it gives me this pop up:



however previous chat logs from 2006 which are plain text files will open fine. as i mentioned, i haven't downloaded anything or changed anything to have triggered this, they just all of a sudden present me with this problem.

i'd be very grateful if someone could shine some light on this for me