Mac Excel 2016 VBA - Workbook.open gives 1004 error - excel

Question

I'm trying to get a macro that works perfectly in Excel 2011 for Mac to work in Excel 2016 for mac. The goal is to have the user specify a folder with .csv files in it, and then the macro loops through all the .csvs, opening each to copy information out of it into another Workbook.
The macro fails when trying to open the first .csv file in the user-chosen folder, with a 1004 error, file cannot be found.
(side note: Earlier in the macro, workbooks.open works perfectly with a user selected FILE)
The macro is huge, so I made a brand new smaller one just to get past this problem. Here is the smaller, test code, which has the same failing behavior:
Sub Test()
Dim folderpath As Variant
Dim filename As Variant
Dim newfilename As Variant
Dim wb As Workbook
Dim newfolderpath As Variant
folderpath = MacScript("choose folder as string")
newfolderpath = Replace(folderpath, ":", "\")
MsgBox (newfolderpath)
filename = MacScript("Choose file as string")
newfilename = Replace(filename, ":", "\")
MsgBox (filename)
MsgBox (newfilename)
MsgBox (Dir(filename))
MsgBox (newfolderpath & Dir(filename))
Set wb = Workbooks.Open(newfolderpath & Dir(filename))
End Sub
All the msgboxes provide expected values.
newfolderpath= the whole path with \ separators.
filename= the whole path and file name with : separators.
newfilename= the whole path and file name with \ separators.
Dir(filename)= just the file name.
newfolderpath & Dir(filename))= the entire path and file name with \
separators.
Set wb line gives:
Run-time error '1004'
'Hard DRIVE\USERS\DAVE\DESKTOP\CSVS\1.CSV'
could not be found.
Clearly the file is there, openable and works.
Any help is greatly appreciated.

Answer 1

Well, I think I found the answer, or at least an answer that works for my project.
I went back to the workbooks.open(user-selected FILE) from earlier in the macro, and discovered it was reading it as "/users/Dave/Desktop/csvs/1.csv". So, even though debug and msgbox were returning backslashes, it was somehow wanting forward slashes (You were partially right, Tim). Additionally, it clearly truncates the name of the Mac hard drive, and starts with the users directory. So, I just modified the variables to match this format, and voila, it worked. For those who are interested, here's the modified code I wound up using:
Sub Test()
Dim folderpath As Variant
Dim newfilename As Variant
Dim wb As Workbook
Dim newfolderpath As Variant
Dim newfp As Variant
folderpath = MacScript("choose folder as string")
newfolderpath = Replace(folderpath, ":", "/")
newfp = Right(newfolderpath, Len(newfolderpath) - InStr(newfolderpath, "/") + 1)
newfilename = Dir(newfp)
Set wb = Workbooks.Open(newfp & newfilename)
Exit Sub
Thanks to everyone that helped.