How should I fix this error: An unhandled exception of type 'System.InvalidCastExcept

[piscis]

How should I fix this error: An unhandled exception of type 'System.InvalidCastException' occurred in microsoft.visualbasic.dll


On this line:

 If UCase$(Microsoft.VisualBasic.Left(lb.Items(i), StrLen)) = ItmStr Then

Here is the Code

Additional information: Cast from type 'DataRowView' to type 'String' is not valid.

]Private Sub SelectString(ByVal lb As ListBox, ByVal ItmStr As String)
        Dim StrLen As Integer, i As Integer

        StrLen = Len(ItmStr)
        If StrLen = 0 Then Exit Sub

        ItmStr = UCase$(ItmStr)
        For i = 0 To lb.Items.Count - 1
            If UCase$(Microsoft.VisualBasic.Left(lb.Items(i), StrLen)) = ItmStr Then
                lb.SelectedIndex = i
                Exit For
            End If
        Next i
    End Sub

    Private Sub txtSearch_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles txtSearch.KeyPress
        Static ItmStr As String
        Dim c As String

        If Asc(e.KeyChar) = Keys.Escape Then
            ItmStr = ""
            lstListMachines.SelectedIndex = -1
        ElseIf Asc(e.KeyChar) = Keys.Back Then
            If Len(ItmStr) > 0 Then
                ItmStr = Microsoft.VisualBasic.Left(ItmStr, Len(ItmStr) - 1)
            End If
            SelectString(lstListMachines, ItmStr)
        Else
            c = e.KeyChar
            If c >= " " And c <= "~" Then
                ItmStr = ItmStr & e.KeyChar
                SelectString(lstListMachines, ItmStr)
            End If
        End If
    End Sub