Index was out of range error when paging in a Nested Datagrid

[Pat]

I have 3 Datagrid nested.
Master
Details
Child
The master has paging (And i'm using the paging inbuilt in the Datagrid)
in the Master DataGrid you select a linkbutton(using commandname) and it
populates the data in the Details DataGrid
(I'm using Dim Filter As String =
CStr(dtgMaster.DataKeys(dtgMaster.SelectedIndex)).Replace("'", "''") to
filter btw the Datagrids)
And the same is what i did for the Child DataGrid.
But i noticed that after selecting a ROW in the Master DataGrid and populate
the Details Datagrid and i try paging it WORKS!!

But after selecting a ROW in the Details Datagrid and i go back to try
paging the Master DataGrid i get the error below
Index was out of range. Must be non-negative and less than the size of the
collection. Parameter name: index
Any ideas?