Take a look at this video https://www.youtube.com/watch?v=yp5kQtQwPNQ&feature=youtu.be

Thanks for your help. I was able to get it working as you described.

It does not need to replace the collection. It will need to make changes to the collection in vb.net and have those changes reflected in the vb6 collection.

I have created a collection class in vb.net to pass a collection from vb.net to vb6 and everything works great. I am now trying to send a collection to a function by reference. The collection is created in vb6 but the function is in a class in vb.net. The function needs to be able to update the collection (thus byRef).

I read setting the parameter ByRef and not ByVal would work but wasn't sure how to set it up. A little tweaking and the vb.net code looks like this:

_
Public Class clsValues

#Region "COM GUIDs"
' These GUIDs provide the COM identity for this class
' and its COM interfaces. If you change them, existing
' clients will no longer be able to access the class.
Public Const ClassId As String = "095dc64d-141f-46f9-9af2-1c5e633b459b"
Public Const InterfaceId As String = "86ec1f14-1ef4-446d-9172-b92cf260cd16"
Public Const EventsId As String = "1605e412-8b11-4ee0-a34c-9ec04464737f"
#End Region

' A creatable COM class must have a Public Sub New() 
' with no parameters, otherwise, the class will not be 
' registered in the COM registry and cannot be created 
' via CreateObject.
Public Sub New()
    MyBase.New()
End Sub

Private mSingleString As String
Public Property SingleString() As String
    Get
        Return mSingleString
    End Get
    Set(ByVal value As String)
        mSingleString = value
    End Set
End Property

Private mStringArray As String()
Public Function StringArray() As String()
    Return mStringArray.ToArray
End Function
Public Function StringArray(i As Short) As String
    Return mStringArray(i)
End Function
Public Sub SetStringArray( ByRef value As String())
    mStringArray = value
End Sub

End Class

The final vb6 code looks like this:

Option Explicit

Private Sub btnTest_Click()
Dim x As Integer
Dim strTest(4) As String
strTest(1) = "abc"
strTest(2) = "def"
strTest(3) = "ghi"
strTest(4) = "jkl"

On Error GoTo err1
    
Dim clsTest As comtest.clsValues
Set clsTest = New comtest.clsValues

clsTest.SingleString = "this is my string"
clsTest.SetStringArray strTest

MsgBox "Single string = " & clsTest.SingleString, vbInformation, "Test"

For x = 1 To UBound(clsTest.StringArray) 'clsTest.UboundStringArray
    MsgBox "Multi string " & x & " = " & clsTest.StringArray\_2(x), vbInformation, "Test"
Next x

Exit Sub

err1:
MsgBox "Error: " & Err.Number & vbCrLf & Err.Descrip

Thank you for the reply It is a typo but this is where the error occurs, see error message at top of message after correction.

Why do i get the error - "Function or interface marked as restricted, or the function uses an Automation type not supported in Visual Basic", when I try to pass a String array from vb6 to a class:Property string array in vb.net? This is the vb6 code:

Option Explicit

Private Sub btnTest_Click()
Dim strTest(4) As String
strTest(1) = "abc"
strTest(2) = "def"
strTest(3) = "ghi"
strTest(4) = "jkl"

On Error GoTo err1
    
Dim clsTest As ComTest.clsValues
Set clsTest = New ComTest.clsValues

clsTest.SingleString = "this is my string"
clsTest.stringArray = strTest   ' <<

This is the vb.net class

Imports System.Runtime.InteropServices

_
Public Class clsValues

#Region "COM GUIDs"
' These GUIDs provide the COM identity for this class
' and its COM interfaces. If you change them, existing
' clients will no longer be able to access the class.
Public Const ClassId As String = "095dc64d-141f-46f9-9af2-1c5e633b459b"
Public Const InterfaceId As String = "86ec1f14-1ef4-446d-9172-b92cf260cd16"
Public Const EventsId As String = "1605e412-8b11-4ee0-a34c-9ec04464737f"
#End Region

' A creatable COM class must have a Public Sub New() 
' with no parameters, otherwise, the class will not be 
' registered in the COM registry and cannot be created 
' via CreateObject.
Public Sub New()
    MyBase.New()
End Sub

Private mSingleString As String
Public Property SingleString() As String
    Get
        Return mSingleString
    End Get
    Set(ByVal value As String)
        mSingleString = value
    End Set
End Property

Private mStringArray() As String
Public Property StringArray() As  String()
    Get
        Return mStringArray
    End Get
    Set(