There is a bug in all 1.5 and 1.6 versions of GrabIt that can cause downloaded files to get stuck in the cache folder. The solution is to update the grouplist:

- Start GrabIt
- Click on the server you are trying to download from in the subscribed groups panel on the left
- Click on the 'Refresh grouplist' button in the top icon toolbar

Now try to download again and see if it works!

Note: GrabIt 1.6.0 and 1.6.1 had another bug that shows the same symptoms. Please upgrade to GrabIt 1.6.2 or higher to solve this problem.