I tested this on one of my programs (it has a form that acts as a command window):
Public cWinz
cWinz='C:\Program files\Winzip\Winzip32.exe'
Run /N3 &cWinz

and works fine

You can add the following
If File(cWinz)
Run /N3 &cWinz
Else
Messagebox('File not found')
* or put other code or message
EndIf

The public variable maybe is not needed for your app, it only was a test.

Mauricio