Error creating thumbnail: convert: memory allocation failed
Fragment of a discussion from Project:Support desk
Now I'm seeing errors like
(Can't contact the database server: User u70717484 already has more than 'max_user_connections' active connections (colton3d.netfirmsmysql.com))
It sounds like your host is pretty messed up.
—Emufarmers(T|C)
Try also increasing $wgMaxShellMemory (for the original issue with convert)