Cubase is refusing to delete my unused media.

Hello.

I’m still currently using Cubase 6.5, though I imagine this problem would relate to any version, as it’s more about my own file system.

I have some old projects that are taking up way too much space on my hard drive. I don’t want to delete them entirely, just remove all the unused media. However, when I go to the pool and click ‘Empty Trash’ after having clicked ‘Remove Unused Media’, I get the error message, ‘Some files were not deleted’. I’ve also tried the ‘Cleanup’ route and, although it easily identifies all the unused media, I’m getting the error message, ‘The selection could not be deleted’.

Why could this be? Any help would be greatly appreciated!

Cheers.
Mason