Problem Importing Playlists from my usb's to my rekordbox library

basically i accidentally deleted my whole database without backing up. ive added all the files back into my collection. 

Every time i try and import a playlist an error pops up saying

'Cannot import the playlist: ________ All songs in the list do not exist in the collection or the list is empty.'

someone help me please! i cannot start all over!

thanks in advance

Richard