Saving projects in TBS 5 (Mac)

I’ve got a Snow Leopard mac, and I made a project. When I open it now, it says:

filename-1.wff.new not found.

I can continue, then there isn’t the audio file (filename.m4a). I delete the empty element and create other. Now it says: Unable to rename filename-1.wff.new to filename-1.wff

How can I solve this?