Invisible file

I have a problem I hope someone can help me with.

In my trash there's a file (a folder) which I
cannot delete. I get an error message saying that
the file is in use. When I open up a terminal and
examines the trash folder, the file is not there.
This has persisted for quite a time, and the darn
folder won't be deleted.

Any tips?

In terminal, type ls -a
this will show invisible files
Also, what Whiteshark said.