I did it like this:
Option Explicit
Sub calcConstr()
Dim FN As String
Debug.Print "FN: " & FN
FN = Application.ThisWorkbook.Path
Debug.Print "FN: " & FN
FN = FN + "\constrCalc3.exe"
Debug.Print "FN: " & FN
Shell FN, vbNormalFocus
End Sub
FN:
FN: E:\...\Downloads
FN: E:\...\Downloads\constrCalc3.exe
That way, you can see how the contents of the variable FN builds up.
The output will appear in the Immediate Window in the VB Editor. If you can't see it, press Ctrl-G.
Are you sure that the full path exists? And that there are no trailing spaces on the folder name(s)? Could it be something to do with permissions? Can you run the .exe file from that folder?
Bookmarks