Okay well this surely works on 5.13
Check your usergroup settings and see how its set.
I get this trying to upload a 160K file to a 125K filesize limit
KIMBERLYrz.jpg (exceeds filesize limit)
Now note this as this is where most people get lost on settings. If a user belongs to multiple usergroups note that the best scenerio is used so if one is set to 0 then that is the filesize limit
Note on the upload page what it says your filesize limit is. If this is your install here then you have other issues http://www.thephonemall.net/photopost/