Hi Richard, I've changed it to eliminate the space - it now reads: ContactNotes: IIf(IsNull([MaxOfDateTime]),"No Contacts",DLookUp("Notes","ContactT","CustomerID=" & [CustomerID] & " AND DateTime=#" & [MaxOfDateTime] & "#"))
However it is still reporting the same error.  Could there perhaps be something wrong in the table its referring to - I just need some guidance on where to 'look'.  I appreciate also, that you don't just 'solve' my problem, you guide , which is fabulous!  

Lynda

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Reply from Richard Rost:

Does the DLOOKUP work WITHOUT being inside of an IIF function?