Hi all,
Thanks for your responses - appreciated. After spending a fair amount of time researching on Google etc... (and coming across those links mentioned by Welsh) prior to posting the initial problem, I was eventually able to resolve it by explicitly granting the account SQL Server is running under access to the user database referred to in the query.
Strange though, as I hadn't needed to do this at all with the previous server. Might be a 2005 to 2008 thing as I am as sure as I can be that all other aspects of permissions were identical between new and old servers.
Anyway, thanks once again for the help.
Regards,
Chris