DataGridView ComboBox Problem

[nomi]

I have a DataGridView containing information of cities of the world. User can retreive records and insert record of cities from DataGridView on selection of country.

For this purpose, i have created four columns in DataGridView dynamically:
1 - S.No.
2 - Country(combo box)
3 - City Code (Edit Box)
4 - City Name (Edit box)

I have created the 'Country' column using "DataGridViewComboBoxColumn" class and populated it with DataTable using DataSource, and hence the DisplayMember is 'Country Name' and ValueMember is 'Country Code' and it is working fine at the moment. Whenever user wants to add a new city, obviously user has to select the country too which i have provided in combobox.

Now the problem is on retreiving data. I am populating the Grid manually i.e. looping row by row and inserting into each cell from a DataSet which is again working fine for all columns EXCEPT the Country column. The program gives me an exception repeatedly stating that "System.ArgumentException: DataGridViewComboBoxCell value is not valid.". I am trying to populate the Country column cell with the Country Code hoping to get the Country Name as the country name is the ValueMember BUT so far it is not letting me do that.

Kindly help me out with this problem, ill be thankful to you.