I think i got it:
Expr1: DLookUp("[overall KPI Score]","[KPI Rating]","[KPI Rating].[Project ID]= " & [project status survey].[project id] & " And [as-of date]= # " & DateSerial(Year(Date()),Month(Date())-1,0) & "#")
it was just a matter of putting the correct characters (#, ", &) in the...