Problem when grouping with spgridview

Question

hi,

I have a problem when trying to group item in my spgridview :

http://cid-412cbc9baadd47dc.office.live.com/self.aspx/.Public/error%20when%20trying%20group.jpg

The gridview take the groupfield to create group but only one item go into each group so i have :

Group A : item 1 Group B : item 2 Group A : item 3

and i want this (wich is the normal behavior of grouping ) :

Group A: Item1 , Item 3 Group B : Item 2

Any idea about this ?