I'm on MU but this should work for all.
Grab the wordpress-mobile-pack.php from the main plugin folder and open in a decent editor : look for
Line 256 copy($source_child, $destination_child);
Add the following directly below
// OldSkool Fix Re-Set The User Permissions chmod($destination_dir, 0777); chmod ($destination_child, 0777);
Uninstall the plugin : then reinstall. When requested over write the existing files.
If you ftp to the themes folders you should now have full access.
Worked for me so hope it helps someone here.