Thanks Dave,
It works from terminal fine now (although not using ./filename - you need to drag + drop the file onto terminal to get the correct path) so I expect it should work on the next synch run.
After doing some digging, the original error in console was:
2005-02-18 00:15:32.812 SuperDuper![1043] ***ERROR OCCURRED: sh: line 1: /Applications/SuperDuper/superduper_sleep_script: Permission denied
2005-02-18 00:15:32.814 SuperDuper![1043] ***ERROR OCCURRED: ****FAILED****: result=32256 errno=1 (Operation not permitted)
So I imagine your 'chmod +x' made the difference by adding 'Execute' permissions.
I'll report back to confirm it worked - but it would be lovely to have sleep/shutdown as options in 'On Completion' in v 2.0
Thanks again.