Is it possible to use FindPrevious when searching with VBA code in a UDF?

I am trying to use VBA for a UDF to manipulate its results based on the "Find" function as it's much quicker than polling every cell looking for results.

I have cut it right back to it's basics to reproduce the error and I still get "Object variable or With block variable not set" error on this part SearchRange.FindPrevious.Address (You have to put a stop on the line and step it to get the error, UDF's just quit out without returning the error outside of debug mode)

Here's the kicker, I get the error when trying to use the UDF in a sheet like so: =testfind("3206-1",E:E) however when I use it in the immediate window in the VBE like so: ?testfind("3206-1",Range("E:E")) i get the correct result of $E$15295 without error.

Code is:

Function TestFind(FindString As String, SearchRange As Range)
Dim ActiveAddress As Range
Set ActiveAddress = SearchRange.Find(FindString)
TestFind = SearchRange.FindPrevious.Address
End Function

Modified with L42's changes and now it works:

Function TestFind(FindString As String, SearchRange As Range)
Dim ActiveAddress As Range
Set ActiveAddress = SearchRange.Find(FindString)
TestFind = SearchRange.Find(FindString, , , , , xlPrevious).Address
End Function

Solution

Edit1:

This code

TestFind = SearchRange.FindPrevious.Address

and this as previously suggested:

TestFind = SearchRange.FindPrevious(ActiveAddress).Address

doesn't work when you use it as worksheet function as what Dan experienced.
Below doesn't directly answer the question but just an alternative.

Alternative: Change the SearchDirection argument in the Find method.

Function TestFind2(FindString As String, SearchRange As Range)
    Dim ActiveAddress As Range
    Set ActiveAddress = SearchRange.Find(FindString, , , , , xlPrevious)
    TestFind2 = ActiveAddress.Address
End Function

Note: You need to add error handler to trap searches with no match found.

How to test:

Sub marine()
    Debug.Print TestFind(4, [A:A])
End Sub