Colorizing analytical data in counties in SSRS 2008 R2

Hello,

When I select the entire US, I can have the states colorized by analytical data.  When I select 1 state and do exactly the same think for the counties, it does not work.  I have a Sql Table with 255 rows.  There are two fields, County and PopulationPerCounty. I select County as the analytical field and COUNTYNAME as the Spacial field.  I select [Sum(PopulationPerCounty)] as the Field to Visualize.  When I run the report, every county is white

Thanks,
Howard