как-то так

[code=vb.net]
Protected Sub GridView1_RowCommand(ByVal sender As Object, ByVal e As GridViewCommandEventArgs)

  Dim rIndex As Integer = CType(e.CommandArgument, Integer)
  Dim thisID As String = Me.GridView1.DataKeys(rIndex).Value.ToString()
[/code]

Хотя не могу сказать, поможет ли это...