Hello,

I succeed to reproduce the GridViewComboboxColumn exception in this forum post:
http://www.telerik.com/forums/nullreferenceexception-4a6181b2453b#cwDrbIqzp0CPxcgh90b4rQ

I attach a sample project, the database (SQL Server 2012 Express) and a video from the exception.

To reproduce:
- Run the project,
- Sort the column "Állapot" descending.
- Click on column and drop down the list.
- Choose an another value, and click very fast twice. On a slow PC is much easier to reproduce the issue. The important thing, that you need select a value from the combobox and select another row very fast. (See the attached video)

I use the latest Trial version of Winforms.

If you have any question, please contact me.

Best Regards,
László

Workaround:

Private Sub gridMunkak_CreateCell(sender As Object, e As GridViewCreateCellEventArgs) Handles gridMunkak.CreateCell
    If e.CellType = GetType(GridComboBoxCellElement) Then
        e.CellElement = New MyGridComboBoxCellElement(e.Column, e.Row)
    End If
End Sub

Public Class MyGridComboBoxCellElement
    Inherits GridComboBoxCellElement
    Public Sub New(column As GridViewColumn, row As GridRowElement)
        MyBase.New(column, row)
    End Sub

    Public Overrides Sub SetContent()
        If Me.ColumnInfo IsNot Nothing Then
            MyBase.SetContent()
        End If
    End Sub
    Protected Overrides ReadOnly Property ThemeEffectiveType() As Type
        Get
            Return GetType(GridComboBoxCellElement)
        End Get
    End Property
End Class