Check the folder you are downloading to. Select it, command (apple key) i keys or go to file menu & choose Get Info ... and at bottom of the window will show permissions. Your account name must be listed and must show Read & Write permissions. Likewise the same applies to your incomplete folder.
Here is an example of adding a different account permissions & giving read & write permissions for that folder: http://www.gnutellaforums.com/attach...ermissions.gif (step 6 in that sample image should have been the admin account.)