Dynamically inserting a new row causes viewstate loading error on postback

[SoftLion]

Hi,
I insert a new DataGridItem during the ItemDataBound event.
The item is correctly displayed. Then I click an "Edit" button to switch a
row in edit mode:
the page won't load with this error "Can't load viewstate...".

What am i doing wrong ?
Maybe I shouldn't insert a new row in this event but another ?
thks.