Access Generic Dictionary Contained Or Nested In Another One?

I have a Generic Dictionary contained or nested as a child in another Generic Dictionary. I need to be able to access the child dictionary objects by key. When I attempt to do this I get the following error:
"Value of type 'System.Collections.Generic.KeyValuePair(Of String, String)' cannot be converted to 'System.Collections.Generic.Dictionary(Of String, String)'."

So it seems that the contained Generic Dictionary is being returned as a Generic KeyValuePair when accessed via a key as opposed to iterating through the parent dictionary in a For/Each loop.

The first section of the sample works OK (using a key to access a string value in a dictionary).
The second section of the code works OK (iterating through the dictionary values in a For/Each).
The third section of the sample is where the error occurs (using a key to access a nested generic dictionary...see underlined code).

Dim td1 As Dictionary(Of String, String)
For Each thisKey As String In td1.Keys
Debug.Print(td1(thisKey))
Next
Dim td2 As Dictionary(Of String, Dictionary(Of String, String))
[Code] .....