Reinstalling WMI
If you experience behavior when using WMI, such as application errors or scripts that used to work are no longer working, you may have a corrupted WMI repository. To fix a corrupted WMI repository, you have to reinstall WMI.

Windows Management Instrumentation - Repair

As for the NET SEND I'm still not sure why you would send that to a user. What purpose does it serve either to you or the user? It is not logged, when the user clicks okay the message is now gone, etc..

We can setup a MessageBox command that would alert YOU as the Administrator about a system if you want which I'm guessing is more of what you're really wanting.