If you are in a wordpress multi site installation you‘ll have to change manually some values in site_meta table.
They are:
1. blog_upload_space – The amount of space a single blog has to upload files to
2. fileupload_maxk – The largest file that may be uploaded (I believe this is in bytes)
3. upload_filetypes – This restricts the MIME type that can be uploaded I believe through the Flash uploader
Many thanks to Sean
http://seanklein.org/2009/06/wordpress-php-upload-information/
