I'm not sure what code you are using. But does the program know you are clicking the right mouse button?
Code:
Public Const WM_LBUTTONDOWN = &H201
Public Const WM_LBUTTONUP = &H202
Public Const WM_LBUTTONDBLCLICK = &H203
Public Const WM_RBUTTONUP = &H205
Public Const WM_MOUSEMOVE = &H200

Private Sub Form_MouseMove(button As Integer, Shift As Integer, X As Single, Y As Single)
  Static lngMsg As Long
  Static blnFlag As Boolean
  Dim result As Long
lngMsg = X / Screen.TwipsPerPixelX
If blnFlag = False Then
blnFlag = True
Select Case lngMsg
'right-click
Case WM_RBUTTONUP
result = SetForegroundWindow(Me.hwnd)
If vbNo = MsgBox("Do you really want to shutdown the program?" & vbCrLf & "Click Yes to quit.", vbYesNo + vbExclamation + vbDefaultButton2 + vbMsgBoxSetForeground) Then
Cancel = True
Exit Sub
Else
Cancel = False
Call DeleteSystrayIcon(picSystray)
Unload Me
End
End If

Case WM_LBUTTONUP
result = SetForegroundWindow(Me.hwnd)
PopupMenu Me.mnumenu
End Select
blnFlag = False
End If
End Sub