Hi Phil,
I've had the same problems in the past. And even when I've been able to upload pics to a gallery on this forum, the quality isn't great.
Ive started uploading the images on an external image hosting site
https://imgbb.com and then posting the links. Much better quality and no problems so far
Doesn't solve the actual issue with the forum, but at least you'll be able to post your pics.
Hope that helps,
Psion