Bumping this up, as I am having the same issue. Is it related to being a newly registered member or low post count?
I am trying to upload a photo into my signature and receive the same message as Buhund_Mom, "cannot save image." My image is smaller than the requirements of 500 x 100. It also looks like I have permissions to upload a photo into my signature.
Text into signature is not a problem.
The same message "cannot save image" came up when I added my avatar, however my photo was added regardless of the message.
Thank you in advance for any assistance!