MacScript for Selecting a Folder doesn't return the path of the selected folder

I'm helping someone with a workbook that should run on both PC as well as Mac.
And of course there is a tiny issue with that

I've written a function SelectFolder() that should serve both Mac and PC:

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As I don't have a Mac myself it's hard to debug this. Maybe someone with a Mac can help me out here.

I'm attaching a sample file with the function in it. Sheet1 has "button" [SelectFolder]. Clicking it should bring up Finder.

EDIT:
the problem seems to be with setting an initial folder path.
Uploaded a updated test workbook with a function taking the initial folder as an optional parameter.
Also updated the code above.

It works for me and returns the selected path.

Hi Rory. Thx for replying.
It seems that with the desktop folder MacScript correctly returns the selected folder path.
But if a specific folder is issued with the parameter it doesn't.
So most likely there's something wrong with the syntax of the folder path coming with the parameter, causing the macscript running into some error and breaking.
Could you check on that, pls.

Finally solved this problem.
For anyone facing the same problem here is the solution.

The culprit is in this code line:

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This variable contained a Posix path (with a slash as separator), but Macscript expects a Mac path (with a colon as separator).
So e.g. "/users/Tsjallie/" should be "Macintosh HD:users:Tsjallie:"

Solution is to convert the Posix path to a Mac path with these code lines:

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For the enthousiasts I'm attaching a workbook with a SelectFolder-fuction which should work on both Mac as well as PC.