I am trying to add two currency columns in a calculated column but am getting a #NULL! error.

This seems pretty straightforward but its my first time doing this in SharePoint.

SharePoint 2010 with Excel Services available.

Have create List with required columns:

Approved Value column Type = Currency 

Pending Value column Type = Currency 

Total Value column 
Calculated (calculation based on other columns) 
Type = Currency
Formula: =[Approved Value]+[Pending Value]

The values in other columns are indeed currency, but the Total shows #NULL! for all items.

I can't see anything done incorrectly.

What should I be looking for to resolve this problem?