The Windows Media Load Simulator (occasionally abbreviated as 'loadsim') tool was created to help stress test Windows Media Services (WMS) servers.  Since WMS does live streaming and uses application specific control messages over RTSP and HTTP using a web server stress tool doesn't really work.  Also, since Windows Media Player actually uses a good bit of CPU to render the audio or video a tool like loadsim is necessary.  It worked well back in the early 2000's, but since the default protocols have changed from MMS to RTSP and the MMS protocol has been completely removed from Windows Media Player 11 and later running loadsim has become a bit dicey on modern systems.  I've had a number of people ask me about how to get it to work, so here are some of the troubleshooting steps that I've used with probably 80% success.

• Windows Media Load Simulator is an old tool that was designed at a time that the MMS protocol was still supported.
• Of course, as per the docs, make sure you have a video file called wmload.asf in the root of your server (typically c:\wmpub\wmroot).
• In certain instances loadsim will connect to the \\servername\c$ share and try to access a file called wmloadsafe.txt.  Try creating this file (add some bit of text to it) and connect to the c$ share from the loadsim machine.
• Because of the MMS protocol being deprecated in later versions of WMP, you should try turning it off.  Even if you are using RTSPT to stress a video, loadsim will still try to use mms://servername/wmload.asf.  There can be odd client namespace issues because of this.  Try the following:
  a) Open a command prompt.
  b) Change to the c:\program files\windows media load simulator folder.
  c) Run the command line:
  
  cscript.exe EnableMMS.wsf 0
  
  The 0 on this command line turns off MMS in the Windows Media Player namespace.