Retaining a formula in a blank cell in half a workbook...

[lilshortiy]

I am trying to make the calculator I am creating able to hold 30 different pieces of information... So far only half of the calculator is full with values. A1 to G9 is filled with data, the rest of the cells, A10 to G29 are blank. I want the cells to have 'N/A' in it.. But it has an error '#N/A'

The formula is as follows
=VLOOKUP(D2,Commission_Rate,2,FALSE)*E2

Commission Rate is the range for the item type, and % of commission recieved depending on tye type...
Help please!
If other forumlas or something can be used please suggest them...

I can post up screen shots of the spread sheets too if that helps

Thanks!!