I got caught with WordPress multisite file upload as I was was trying to upload some photos from UBP Global and Board Moderators Year End Party. I was getting the prompt “…exceeds the maximum upload size for this site.”
My first attack to solve the problem was to check post_max_size at the load PHP configuration file. Then tried uploading again, I was prompted with the same error. Second solution, to update the .htaccess file to suit my requirement. Again, it did not solve the problem.
Then I finally get into ./wp-admin/network/settings.php which provide the setting for Maximum Upload Size. I changed the setting then mu uploads was successful.