Error:
The file is corrupt or has an incorrect extension. Please check the file and upload again.
Solution:
$wgVerifyMimeType = false;
Other checks are to make sure the following are set:
$wgEnableUploads = true;
$wgFileExtensions = array( ‘doc’, ‘xls’, ‘png’, ‘gif’, ‘jpg’, ‘jpeg’, ‘ogg’, ‘zip’);
in LocalSettings.php which should be in your root wiki directory (not config).
See also: http://meta.wikimedia.org/wiki/Help:Images_and_other_uploaded_files#Troubleshooting_File_upload
