Unexpected Cast error in 'For Each'

Hi,
I'm converting some VB6 code to .NET and I'm having an error occur when I try to loop through a collection of objects:

'An unhandled exception of type 'System.InvalidCastException' occurred in SiD.exe

Additional information: Specified cast is not valid.'

It basically doesn't like the 'For Each' statement in the simplified code listing below:

Code:

---

Sub PopTreeView()

    { Other Declarations }
    Dim oServer As cServer


    For Each oServer In gcolServers

    { Processing Code }
   
    Next

 End Sub

---

The gcolServers variable is a collection of cServers, so its got me confused as to why the cast is invalid. As far as I understand it the enumeration within a collection is inherited in .NET so I don't need to code for it specifically like in VB6. Here's the object and collection definitions (simplified for space) anyhow:

Code:

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Public Class cServer

  ' Local variables to hold property values
  '
  {Local variable defs}


  {Property gets and sets}


  Public Sub New(ByVal intServerID As Integer, _
                  ByVal strServerName As String, _
                  ByVal strServerDescription As String, _
                  ByVal intLocationID As Integer, _
                  ByVal intOSTypeID As Integer, _
                  ByVal strNotes As String, _
                  ByVal intModelTypeID As Integer, _
                  ByVal strSerialNumber As String, _
                  ByVal strSAPassword As String, _
                  ByVal strSystemAdminPassword As String, _
                  ByVal strSQLSSAPassword As String, _
                  ByVal strMachineAdminPassword As String, _
                  ByVal clDrives As colDrives, _
                  ByVal clDatabases As colDatabases, _
                  ByVal intGroupID As Integer, _
                  ByVal intGroupOrder As Integer, _
                  Optional ByVal bIsPwdDirty As Boolean = False, _
                  Optional ByVal bIsDetDirty As Boolean = False)

    ServerID = intServerID
    ServerName = strServerName
    ServerDescription = strServerDescription
    LocationID = intLocationID
    OSTypeID = intOSTypeID
    Notes = strNotes
    ModelTypeID = intModelTypeID
    SerialNumber = strSerialNumber
    SAPassword = strSAPassword
    SystemAdminPassword = strSystemAdminPassword
    SQLSSAPassword = strSQLSSAPassword
    MachineAdminPassword = strMachineAdminPassword
    Drives = Drives
    Databases = Databases
    GroupID = intGroupID
    GroupOrder = intGroupOrder
    IsPwdDirty = IsPwdDirty
    IsDetDirty = IsDetDirty

  End Sub

End Class


Public Class colServers

  Inherits System.Collections.DictionaryBase

  Public Function Add(ByVal ServerID As Integer, _
                      ByVal ServerName As String, _
                      ByVal ServerDescription As String, _
                      ByVal LocationID As Integer, _
                      ByVal OSTypeID As Integer, _
                      ByVal Notes As String, _
                      ByVal ModelTypeID As Integer, _
                      ByVal SerialNumber As String, _
                      ByVal SAPassword As String, _
                      ByVal SystemAdminPassword As String, _
                      ByVal SQLSSAPassword As String, _
                      ByVal MachineAdminPassword As String, _
                      ByVal Drives As colDrives, _
                      ByVal Databases As colDatabases, _
                      ByVal IsDetDirty As Boolean, _
                      ByVal IsPwdDirty As Boolean, _
                      ByVal GroupID As Integer, _
                      ByVal GroupOrder As Integer, _
                      ByVal sKey As String) As cServer

    Dim oServer As cServer

    ' Add the properties to the collection as a new Server Class
    '
    dictionary.Add(sKey, New cServer(ServerID, _
                                      ServerName, _
                                      ServerDescription, _
                                      LocationID, _
                                      OSTypeID, _
                                      Notes, _
                                      ModelTypeID, _
                                      SerialNumber, _
                                      SAPassword, _
                                      SystemAdminPassword, _
                                      SQLSSAPassword, _
                                      MachineAdminPassword, _
                                      Drives, _
                                      Databases, _
                                      GroupID, _
                                      GroupOrder, _
                                      IsDetDirty, _
                                      IsPwdDirty))

    ' Return the object created
    '
    Return dictionary.Item(sKey)

  End Function


  Public Sub Remove(ByVal strKey As String)

    ' remove the cServer Class from the collection for the supplied Key
    '
    dictionary.Remove(strKey)

  End Sub


  Default Public Property Item(ByVal strKey As String) As cServer

    Get
      Return DirectCast(Dictionary.Item(strKey), cServer)
    End Get

    Set(ByVal Value As cServer)
      Me.Dictionary.Item(strKey) = Value
    End Set

  End Property

  Public Sub New()

    MyBase.New()

  End Sub

End Class

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Anyone got any suggestions?

Rob