Error uploading to My Gallery

[Coolio]

I'm getting an error msg when I try to upload a .jpg file to My Gallery.

I've attached a screenshot.

I have the option to attach files to a post, but I don't have this option available in Messenger, which is what I was trying to do in the first place (before I tried to upload to My Gallery).

I've been through all the settings but may have missed something obvious!

I use a Macbook Air.

Any help would be appreciated.

Ta,

Dave