can't delete record when using objectdatasource and GridView

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Hi Guys, I have a simple Edit,Update Gridview and i'm using
ObjectDatasource with dataset generated and TableAdapters I can do an
update no problem.
But can't get my delete to work. When i look at the parameters sent to
the store proc it all contains NULL.
I came across a solution using setting DataKeyNames but i don't have a
primary Key ID on the table.The parameters i have are
theyear,themonth,code and i want to delete based on those paramters
which i have in my
DeleteParameters tag. How can i accomplish a delete in such sceanrio?
Thanks in Advance