Initial Download (Filter)Error: R/3 to CRM 4.0

Hello

I want to bring customer master data from SAP R/3 to SAP CRM 4.0 using filter on country code 'US'. While creating filter i get this error- 'Object CUSTOMER_MAIN does not allow filter on KNA1.LAND1'. I am i doing any thing wrong. Can I create a filter for country codes, and account groups.

Good Day.

Thanks

Jay