did you host it on OSA or did you use a host like village photos or boomspeed (examples) to host it ?
chances are if you havent signed in to them for a while the accounts suspend/or cease to be until you sign into them again (might need you do that once a month or so) and you may need to reupload your sig from your PC.
Id try it again in the user CP section and see if it works.
There has been some updates to the forum recently so it may well be that you need to reupload your sig in the user CP section. I had to do this not so long ago and have had no probs since.