Sucks but basically its like this:
If you transfer a game via FTP - DELETE via FTP
If you rip game from disc in Multiman - Delete through multiman
Whatever way you add the game, is the same way you want to delete it otherwise the space that was freed up will NOT BE RECOGNIZED BY YOUR PS3.
This is a known problem with PS3's. I remember an old thread where this was discussed.
Your only option to have the HDD read the free space would be to format the HDD, and if you do that you will need to make sure to back up everything you wish to keep.
Originally Posted by sidthekool
As far as I know, my ps3 has never had an undetected error.