Object ToString in DatagridView

A datagridview is populeted by a List(of cInfo) The Datagridview Columns are
bound to properties of cInfo. Some of the properties are object types (for
example cByteInfo) and for that the cByteInfo class as a Overrdes ToString
who represent the class State. This is working fine and like i need. But now
i want to edit the grid and also the column who is bound to a object. By
validate so a cell i recive of cource a FormatException (Invalid conversion
from System.String to cByteInfo).
Cane somebody help me to find a solution for this probleem.

Best Regards
Vic