Check SharePoint Server block list settings. SharePoint Server blocks files with the suffixes you specified. Use the SharePoint Server Central Management Page to modify the configuration.
To remove a file blocking configuration from SharePoint Server:
  1. Select Security Configuration.
  2. Select Define blocked file types from General Security configuration.
  3. Check the extension names listed in the dialog box. Any extension name that is included will be blocked by SharePoint Server when it is uploaded or downloaded.