jpeg problem

I've been trying to figure this out on my own and I checked memories and I'm stumped. I use PSP8 & run winXP. Lately if I save an icon as a jpeg it won't post. Instead I have to save as a png. 99% of the time this is not a problem, I prefer to use png anyway. However, I sometimes make icons for a friend who had a MAC and he can't use png. This means I send my icons to yet another friend who saves and converts them to jpegs for him. Can anybody help me figure out why my jpegs no longer work?