I want to turn off the "Unable to set cell value" pop up box. 

I bound the XamDataGrid to an observable collection and turned on exceptions and off notification like this:

<igDP:

XamDataGrid x DataSource="{Binding Members, ValidatesOnExceptions=True, NotifyOnValidationError=False}" ...

I have ViewModels for the window and ViewModels for the Members in the list.
in the MemberViewModel on one of the properties that is bound to the grid I throw an exception if the value does not pass validation logic. 

The Grid displays a pop up: "Unable to set cell value".  It does not use the message from the exception. 

I would like to turn off that pop up and provide my own before I throw the exception or something like that.  How can I do this?