Generic Inquiry Results Grid Issue

I have a Generic Inquiry that will display the Box Size and Qty used by month for the current year. 

In the Results grid I have am using SOShipment.ShipDate_Month as the Month field. The GI works fine and I have a Pivot Table that works very nicely. 

I’ve been asked if I could possibly add the month name (January, February etc) in stead of the month number (1,2,3...)

So I modified the SOShipment.ShipDate_Month in the Result Grid as follows;

=iif([SOShipment.ShipDate_Month]=1,'January',iif([SOShipment.ShipDate_Month]=2,'February',iif([SOShipment.ShipDate_Month]=3,'March',iif([SOShipment.ShipDate_Month]=4,'April',iif([SOShipment.ShipDate_Month]=5,'May',
iif([SOShipment.ShipDate_Month]=6,'June',iif([SOShipment.ShipDate_Month]=7,'July',iif([SOShipment.ShipDate_Month]=8,'August',
iif([SOShipment.ShipDate_Month]=9,'September',iif([SOShipment.ShipDate_Month]=10,'October',iif([SOShipment.ShipDate_Month]=11,'November',iif([SOShipment.ShipDate_Month]=12,'December',''))))))))))))

When I run the GI I get an error that reads “Case expressions may only be nested to level 10.”

If I remove iif([SOShipment.ShipDate_Month]=11,'November',iif([SOShipment.ShipDate_Month]=12,'December', from the field and run the GI it displays the name as it should.

My question is, is there a work around or better may to Display all the Month Names?

Thank you!