Dimension Property

I’m trying to map one dimension in my transaction list to another using the lastnotblank function: 

‘Pigment Dealer Model’ is the transaction list and ‘Dealer Type’ and ‘Dealership Id’ are both list properties; sometimes when I use the lastnonblank function it will work and other times, I get the error below: 

Is there a reason this function would be working sometimes, and not other times? When it works it produces this: 

Any help would be much appreciated and please feel free to ask for more detail if needed.