dataview.rowfilter problem

Hi, my program suspends approximately 8 seconds when assign a specific value to rowfilter method. The difference of this special value from others is that number of returned rows is zero when it is assigned to RowFilter. Unfiltered table has 400 rows and 2 columns. I tried a new sample with only this table and one dataadapter and the same SQL select statement. But new program is very fast and no has any delay time. What the problem on RowFilter may be? thanks, erkal