Thank Guys.
Josephur, as a rule you're right. At the time of writing the program, there was something I specifically wanted to put in the Program Files folder. However, I've re-written the program to avoid it, now. I was curious (and somewhat irritated) that, as administrator, I couldn't submit a file to the folder. (I even tried saving a simple Notepad file there, and got the same result!)
I did, temporarily get around it, though, by checking the 'Run this program as an administrator' checkbox in the 'Compatibilities' tab in the 'Properties' of the program. This allows write access to that folder in the program, but does cause a admin warning to pop up every time the program is started.
As I said, I've changed the way the program operates, so the question is, now, academic. But many thanks for the replies. Much appreciated.
Matt