My problem is when using the "measure Area" tool on the toolbar I get the correct value but when using the field calculator in the Layer Attributes the area is very different including -ve areas. Both the project and layer are using a UTM CRS. Using version 2.0.1
Note that identify tool and field calculators use different methods to calculate areas:
Vector -> Geometry Tools -> Export/Add geometry columns
lets you choose if measurement of the new columns shall be in layer CRS, project CRS or ellipsodial (which the identify tool uses).