My MSU knob .. if I left click the "+" to rotate knob CW from STBY to Align ... it will not move.

 

I can left click the "-" to rotate it back to OFF.

 

MSU is on Overhead panel, upper left.

 

Using:

// Panel configuration file.
// TinMouse II Boeing 737-200 for FS2004
// Widescreen (16:9) with optional CIVA INS and SP177 Autopilot
// Copyright © 2005-2011  Richard Probst and Robert Scott.
// Version 1.40
// Released as freeware under the Artistic License v2

My error, it is working normally.

I had failed to pull the knob first.