BRIAN50 Thanks for the advice.
Maintenance was installed over a clean install of Leopard (10.5.1) on a new internal hard drive so no previous version .plist file present. I downloaded the app twice and attempted to save preferences six times before giving up.
Deeper was installed first and appears to work perfectly. Removing the Deeper .plist file, just on the off-chance, made no difference to Maintenance. It simply crashes when attempting to save preferences.
(Version 1.2.0b1)