Can't delete backup files from Time Machine

I went into Time Machine (the universe) and deleted a large item that I'd also just deleted from the Desktop (a copy of the Fusion Virtual Machine folder) but it wouldn't let me delete Virtual Machine backups from the Documents folder. Why is that?

Can you quickly explain exactly how you tried to delete a file from within Time Machine ?

Cheers ... McBie

Thanks. Problem has been sorted . . . and there wasn't one!!