Gridview filtering by combobox

Hi All,
I have 1 aspxGridview which is when user select the description on combobox; gridview will be refresh and gridview only display data that have related with combobox selection.
If i have only 1 word ex: 2009; the filtering look like ok.  But if i change the data filtering to w.e.f 2009, data can't listing out.  Y this problem happend?..
Pls help me. 
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