Datagridview Error

Question

Dear Friends,
I have Gridview1 in which i fill data for Items & its quantity and packet_size which is (500ml,200ml,...etc) according to the Items selected in Gridview.
there are 2 combo box in Gridview for Items and Packet size.
the records are been saved properly, the error is whn i get the data(Record) from another Gridview2 to fill in Gridview1 only Packet_size(500,200ml) is not showing up.
The Error is been shown in Data_error event of gridview:
DataGridViewComboBoxCell value is not valid".

Thanks & Regards,
Aamir