System.InvalidCastException: Cast from type '_ComObject' to type 'String' is not valid

Hi,

I'm using a function to retrieve properties from a DirectoryServices object.

Unfortunately, the function fails whenever I trry to assign the object properties "accountExpires" to a string value with the error: System.InvalidCastException: Cast from type '_ComObject' to type 'String' is not valid.

The function I am using is as follows:

Public Function GetObjectProperties(ByVal DN As String, ByVal PropertyName As String) As String

        Dim strOutput As String

        Dim DE As New DirectoryEntry
        DE.Path = "LDAP://" & ServerName & "/" & DN
        DE.Username = AdminUsername
        DE.Password = AdminPassword

        Try

            DE.RefreshCache()
            If DE.SchemaClassName = "user" Then

                strOutput = CStr(DE.Properties(PropertyName).Value)

            End If

        Catch ex As Exception

            'TODO: Raise an error
            strOutput = "Exception! Input DN was = " & DN & "<BR>The error was: " & ex.ToString


        End Try

        Return strOutput
        DE.Dispose()

    End Function

I know this function works, as it WILL retreive other properties, such as 'CN'. But it dies on trying to retrieve the expiration date.

Cheers