Hmmmm, very very strange! Glad you got it sorted...
here's some more info for others with this problem:
Just to run through how deleting works - like a book, your hard drive has a table of contents, and lots of chapters with "data".
When we normally delete something, it only removes the TOC entry. This means the data is still really there on the hard drive, but there is no reference to that area. That area is therefore considered blank.
This explains how the police catch people looking at naughty photos from the web that they thought they deleted!
Anyway, ... from this if your TOC data was deleted for the 6GB, the hard drive space should show that there is an extra 6GB. This has not happened. I would therefore suggest that the TOC links have not been removed correctly.
Get yourself some sort of recovery tool ... PC Inspector, OnTrack Data Recovery, or even PQ MAGIC (in fact I would suggest the latter). These can do all sorts of checks, deletes, etc etc.