I called the method below and got the message below. The way I read that is that the method has resulted in more than one record, which would have caused the exception, each having a unique PK. I have checked the query and it does exactly as desired, which is filter for one specific record.

If (Me.TblDocMasterTableAdapter.FillByChangeID(Me._MasterBase5_0DataSet.tblDocMaster, glbintChangeID)) = Nothing Then
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Also, of note is that this called from a DGV in another form, as seen below

    Private Sub dgvList_CellDoubleClick(sender As Object, e As DataGridViewCellEventArgs) Handles dgvList.CellDoubleClick
        'Define variable values from record
        glbintChangeID = CInt(Me.dgvList.Rows(e.RowIndex).Cells(1).Value.ToString)
        glbintSiTechID = CInt(Me.dgvList.Rows(e.RowIndex).Cells(0).Value.ToString)
        glbstrTitle = CStr(Me.dgvList.Rows(e.RowIndex).Cells(2).Value.ToString)
        glbstrRevision = CStr(Me.dgvList.Rows(e.RowIndex).Cells(3).Value.ToString)
        If glbstrObject = "Document" Then
            Select Case glbintForm
                Case = 1
This is of note because if I select the first row displayed in the DGV the exception is not thrown. If I select any other row below that the exception is thrown.