VLOOKUP/formula produces #N/A

I am using this formula:
=IF(O6>0,"",(VLOOKUP(A6,Material!A2:G43,7,FALSE)))/2000*O6

and it produces #N/A in the cell that contains this formula. If cell A6 has an item selected in it I made from data validation-list then the output is $0.00.

How can eliminate anything from showing if the list is blank in cell A6?Thanks for helping!!