Can't change values of items in a collection

When I try to change the value of items in a collection, I get the runtime error '424' Object Required.

Windows 7 Home Premium
Microsoft Office Professional 2010
Excel version: 14.0.7116.5000 (32-bit)

Here's the test code (not sure how to make it appear like code)

Public Sub test()

Dim txtdata As New Collection

txtdata.Add "text 1"
txtdata.Add "text 2"
txtdata.Add "text 3"

txtdata(3) = txtdata(1) & txtdata(2)

End Sub


When I run this sample code, I get the runtime error '424' Object Required on the line reassigning txtdata(3). When I look at the collection in the watch window, it shows that each member of the collection is a Variant/String type.

I have tried using "Set txtdata(3) = txtdata(1) & txtdata(2)", and get the same error.

Any thoughts are greatly appreciated.
Thanks

Thanks GC, this solution works well.