I am getting a mix aggregated/non-aggregated error when I put a calculation that works well in an additional if statement with Size(). I am not able to resolve. Any help is much appreciated.

This calculation works well:

If {Fixed [Course Number1]: COUNTD([Facilitator])>2} Then {FIXED [Course Number1]: AVG([C:#6.0])} ELSE 0 END

In order to make Hierarchy column totals work when collapsed, I need to add a Size() test. This creates an aggregated/non-aggregate error. I think I want something like this

If size()>1 then 

  (if {Fixed [Course Number1]: COUNTD([Facilitator])>2} Then {FIXED [Course Number1]: AVG([C:#6.0])} ELSE 0 END) 

else 

  (if {Fixed [Course Number1]: COUNTD([Facilitator])>2} Then {FIXED [Course Number1], [Course Start Date]: AVG([C:#6.0])} ELSE 0 END)

END

All help is very much appreciated. If needed I'll mock up a sample data set but I guess that the solution will be obvious to some of you! Thanks in advance. Matt