You should be fine converting to a jpg if you're just uploading a still pic for your avatar. The jpg you're dealing with my have a problem, try opening it with your PS, copy and paste it into a new file, and re-save it as a jpg again. Make sure your height, width, and file size are right for the site. I've noticed with mine, PS 7.0, that when you save a jpg and it tells you it will be about 30k, it actually ends up being like 34, so save it smaller than you think you need it.