Adding a calculated item to a pivot table - problem encountered

I am using Office 2010 and have been trying to add a calculated item to a pivot table but am being greeted with the error
"There are too many records to complete this operation"
The data source is a small area (28 columns by 132 rows) and I am only trying to achieve a simple result in the calculated item
adding 2 existing items together to get a new item so that I can filter the pivot table on this new item rather than the previous 2.

e.g.
Calculated Item

Name: Pear
Formula: =Apple + Orange
(where apple and Orange are existing)

There are no formula in my source data either so it should be quite simple.
I have noticed that the new item has been created but the error still exists am I doing something wrong?
Any help would be greatly appreciated as otherwise I will need to put formula in my source data which I find looks messy and means
you also need to protect them etc...

many thanks

James

Hi JosephP

Thanks for your response, here is the attached data plus pivot

I want to be able to filter the pivot table to make it easier for an end user

so that apple and orange in the 'cust' column of the pivot could be filtered together

and just appear as one item. I initially thought that a calculated item would do the job

Ok thanks Joseph, I'll give that a go