VS2005 : Datagridview : At Least One Object Must Implement IComparible

in my datagridview, i have a column where, depending on values in other columns, I declare a new DataGridViewImageCell, set the image and then attatch it to the grid (brief example below):

Dim cell As DataGridViewCell = New DataGridViewImageCell
Dim img As Image = imgList.Images("comments")
Dim i as Col = 1
cell.Value = img
grdHeldOrders(column.Index, i) = cell

When i click on the column header in question to sort, I get the exception "At least one object must implement IComparible". I kind of guess this because certain cells are different types but I'm not sure how to get around the problem and where to implement IComparible. Does anybody have any examples?