Data Source - Bad Date

hello,

I am trying to set a new value for a matrix cell, and the datasource of this cell is a date data type, from OBNK table and DueDate column. When I set a new value, a get this error: "Data Source - Bad Date"

This is the source code:

OGrid.Columns.Item("2").Cells.Item(ll_i).Specific.Value = ls_field

ls_field is a string variable.

Thanks.

Julia