Many thanks to you both - I had already thought to use 'auto exec' when I read your answer Frothingslosh(!)
TJPoorman, you asked Why? - my client wants to be able to create individual customised databases from within the basic database - so I was setting properties for a new database. What I DID discover, that I had not realised, was that some database properties don't automatically exist so can't be set for a new database until they have been added to the properties collection.
There is always something new to learn in life!!