I have a grid that is bound to a table of the biz object that is not the default. It has an additional column which is not in the biz object but I need to allow the users to edit from the grid so I can do something with that value when the grid values are saved. I am getting the following error when the dataset is being bound to the grid control: " 'ddlDamageReason' has a SelectedValue which is invalid because it does not exist in the list of items. Parameter name: value"

When I create the dataset, I have tried setting the value of the underlying column to NULL , 0 and blank but all generate this same error.

Here's is the definition of the drop down list in the grid.
mm:mmDropDownList ID="ddlDamageReason"
BindingSource="DamageReason"
BindingSourceDisplayMember="Reason"
BindingSourceValueMember="DamageReasonID"
BindingValueSource="IssueDetail"
BindingValueSourceMember="OpenIssues.DamageReason"
SelectedValue=Bind("DamageReason")
UserFieldName=""
AddBlankEntry="True">


The binding source has 2 fields: DamageReasonID and Reason. The BindingValueSource biz object, IssueDetail, does not have a column DamageReason but the table I am using for this mmGridView, OpenIssues, does have that column.

Does anyone have an idea why this isn't working? Is this a limitation of web forms or am I just tired and missing something? TIA.