Hi, I found a solution to ignore the error fields so that the sum function works.

My sum total is in column 3 & my lookup values are in column 2.
=IF(ISERROR(C2),0,C2)

This is stating that if the cell ISERORR due to being blank or value error in the lookup then fill field with 0, if the field is not blank then use the value found in the cell. I hope this helps you.

cheers
Sven