"Not applicable (list geometry)" in a Bex Condition

Hi All:

I have defined a condition in a query in Bex.

Basically I have formula that calculates the difference between two key figures.

The condition is very simple: When this difference is positive (> 0), then the record should be listed.

I execute the query. When I try to navigate through the result set, the condition is no active anymore and I receive the message "Not applicable (list geometry)".

What can I check?

Thanks.