I have my alt.binz folder (and temp folder) located on a different drive than my download folder. However, because my computer isn't fast enough to decode at the same speed as it downloads, if my system drive fills up before it has a chance to decode things to the download folder drive, Alt.binz freezes up because there is no more space left on the temporary folder drive.
Basically I think the 'pause if free space on destination below' should also monitor the temporary folder drive to avoid the crashes. This way, the queue will then be paused, some of the files will be decoded and moved to the download folder drive, and then the queue can resume.