I tested with a public folder and it works the way you did in your first post.
Could you please run the following script so we are sure there is no old version of the UDF flying around?
Global $oOutlook = _OL_Open()
If @error <> 0 Then Exit MsgBox(16, "OutlookEX UDF", "Error creating a connection to Outlook. @error = " & @error & ", @extended = " & @extended)
MsgBox(0, "AutoIt version", " AutoIt version: " & @AutoItVersion)
Global $aVersion = _OL_VersionInfo()
Global $aResult = _OL_FolderTree($oOutlook, "Configuration.Admin@company.com")
If @error <> 0 Then Exit MsgBox(16, "OutlookEX UDF", "Error creating folder tree. @error = " & @error)
Please post the result of the MsgBox and the _ArrayDisplay.