Many thanks Jason,
Everything went very smoothly - a very slick app, this.
Linking is already relative to document, and the pages were all up and running smoothly live - having done them in CS3, and even with the 'Where?' column. So I guess that CS4 is a little stricter. Would that column header have caused the Visual C++ Runtime error? Probably, as all is well now.
Anyway, I have amended the column name throughout the admin pages and in the SQL - I like to find out the correct way of doing things, and appreciate your taking the time to explain this - it will undoubtedly save me from certain anguish on future projects.