Thanks to all good monks for their helpful suggestions, but especially to Jenda for responding quickly and helping me dig myself out of a hole - and on a Sunday afternoon/evening no less!

In the end I had to recreate the user account with domain admin permissions. I also had to re-enter the password in the Service Setup Dialog (per MS!), despite not having changed it. I found some rather vague notes about this, on a number of web pages, including some MS help sites.

Jenda - Win32::Daemon::Simple rocks! It makes Dave Roth's excellent Win32::Daemon a joy to work with.