GETPIVOTDATA and (blank)

I have created a spreadsheet which has two pivot tables in it on separate
sheets. In addition there is a summary sheet which I use the GETPIVOTDATA
function to extract data from the pivot tables referencing adjacent cells for
the Manager and Rep ID's. The original data includes some rows without ID's
in either the Rep or the Manager fields resulting in some "(blank)" entries
on both pivot tables. Where this has happened on the first table I have
entered "(blank)" in my reference cell on the summary sheet and the data is
extracted as nomal.

When I apply the same logic to extracting the data from the second pivot
table I'm getting a #REF! error. I can see no differences between the two
pivot tables (apart from the data obviously).

Any suggestions would be greatly appreciated.