The message box has already been shown in the Record row, however there seems to be a bug in WebGrid that caused a different behavior for NewRow row type. A bug report has been submitted to the developer. We will inform you if there is any progress or update regarding this issue.

In order to remove the cell value of the linked combo column, you will need to use the AfterItemSelected event handler of the parent WebCombo to set the cell value and text to empty string. Here is the snippet, Division column and SubDivision column is linked:

function wcDivision_OnAfterItemSelected(controlId)
{
	var wcDivision = ISGetObject(controlId);

	var grid = ISGetObject("grdObj");
	
	grid.GetSelectedObject().ToRowObject().GetCell('SubDivisionID').SetValue("", true);
	grid.GetSelectedObject().ToRowObject().GetCell('SubDivisionID').SetText("");

	return true;
}

We have recently released WebUI Studio 2009 R2 Service Pack 1 which includes the fix for this issue. Please click here to read the official press release.

You could also read which fix or enchancement included in the latest build by visiting the support page and clicking the control name located on the Right Pane "Latest Builds".