SSMS to SSRS issue

Good morning,

I always have issues with SSRS when I step away from it for a while! I guess that's the joy of being a jack of all trades, master of none :).

Anyway, the following SQL runs fine in SSMS and gives me expected results: -

But when I try to create a report in SSRS, I get the following error: -

I am wondering if the issue is a setting in SSRS more than a SQL issue but can anyone see anything obvious here?

(Please dont comment on my very limited SQL skills - its still a bit of a dark art to me!).

Thanks in advance

Glenn