Return cell value based on criteria of 2 columns

Hi all,
I've searched, researched and scratched my brain on this and I can't seem to get this formula to work. I'm using nesting sumproduct formula, but this is not working.

What I'm trying to do is populate a table in one worksheet, using data from another worksheet....the catch - The formula must look up 2 values in columns A and B and return the value in column C.

Attached is the sample of what I'm trying to do, and a sample of the formula I'm trying to use.

All help would be greatly appreciated.
Cheers,
Fatnslow