If you're still having issues, I would first try running alt.binz as administrator and see if that works. If it does, it could be a permissions problem (hence the Access Denied error).
Open alt.binz as per normal, go to Task Manager and see which user the process is running under (under the Processes tab). Then go to your download/unrar folder and confirm that user has write/full access to that folder. If that user doesn't have permission, grant the access.