jsAPI2.1 'query.geometry' doesn't work with arcgis server9.3.1 ?

[byebye]

Hello everyone:
    Now I encounter a problem:
       I use queryTask to query a polygon layer, when I use 'query.where' ,it works fine;when I use 'query.geometry = graphics.geometry ',it doesn't work !  I copy the example 'Query map with buffer polygon' ,just change the layer ,it still doesn't work !
       Why?

        I use arcgis server9.3.1 as the server service.

       Can you help me? Thanks a lot .