Sounds like you are still having problems as I explained in post #2 or you did not add the quotes as I demonstrated in post #4 as I built s.
Paul asked you to post your command line string. I showed you how to get that via the Debug.Print line in post #4. It puts the result in VBE's Immediate Window. Of course the Dir() commands that I used there might have shown the problem. Another way to get your command line string correctly would be to do the Run manually. Win+R opens a dialog to Run shell commands. Of course you would need to add the quotes around the paths there as well. You could copy and paste the string from the Immediate Window to that Run Window. e.g.
"c:\Program Files (x86)\Minitab\Minitab 18\mtb.exe" "C:\myfiles\MiniTab\MiniTab.MPJ" 1
Of course you don't really need the 1 for an MPJ file. An mtb file would expect the number of runs. I had to guess what type of "file" you wanted to pass to mtb.exe in post #4.
So, this is mostly the same as post #4 but I show you how to get the Desktop path and to run pass the MPJ file to mtb.exe.
Sub Main()
Dim exe$, mpj$, q$, s$, d$, p$
d = CreateObject("Wscript.Shell").Specialfolders("Desktop") & "\"
exe = "c:\Program Files (x86)\Minitab\Minitab 18\mtb.exe"
'mpj = d & "Myfile.mpj"
[F7] = "C:\myfiles\MiniTab\MiniTab.MPJ"
mpj = [F7]
q = """"
If Dir(mpj) = "" Then
MsgBox "mpj's path does not exist.", vbCritical, "Macro Ending"
Exit Sub
End If
If Dir(exe) = "" Then
MsgBox "mtb.exe's path does not exist.", vbCritical, "Macro Ending"
Exit Sub
End If
s = q & exe & q & " " & q & mpj & q & " 1"
Debug.Print s
'"c:\Program Files (x86)\Minitab\Minitab 18\mtb.exe" "C:\Users\Ken\Downloads\CementData.mtb" 1
'"c:\Program Files (x86)\Minitab\Minitab 18\mtb.exe" "C:\myfiles\MiniTab\MiniTab.MPJ" 1
Shell s, vbNormalFocus
End Sub