Public Declare Function ShellExecuteA Lib "shell32.dll" (ByVal hWnd As Long, _
  ByVal lpOperation As String, ByVal lpFile As String, ByVal lpParameters As _
  String, ByVal lpDirectory As String, ByVal nShowCmd As Long) As Long
 
[...]
 
ShellExecuteA Form1.hWnd, vbNullString, "Calc.exe", vbNullString, "C:\", _
  SW_SHOWNORMAL 'Klappt!
 
ShellExecuteA Form1.hWnd, vbNullString, "Regedit.exe", vbNullString, "C:\", _
  SW_SHOWNORMAL 'Klappt auch!
 
ShellExecuteA Form1.hWnd, vbNullString, "Regedit.exe /s " & Chr$(34) & FileName _
  & Chr$(34), vbNullString, "C:\", SW_SHOWNORMAL 'Klappt nicht!

ShellExecuteA Form1.hWnd, vbNullString, "Regedit.exe", "/s " & Chr$(34) & _
  FileName & Chr$(34), "C:\", SW_SHOWNORMAL