There are a number of problems you face that you are not aware of, and a number of ways to go about fixing them. For one, you have choosen a simple bat script, and then attempted to execute it under the assumption it's valid executable code, which it isn't.
To go about doing what you want (running code to shutdown/message/ect), I suggest you look into two methods:
1. CodeDom, which will allow you to build a separate application, from your current application, with custom code (with this you can use simple vb code to perform a shutdown using the shell script)
2. Look into a bat --> exe converter. To perform a conversion like this, you will have access to two methods. The first method, one that I recommend, would be to obtain an already built converter that accepts command line arguments (they are easy to find), and then have your program run the bat file through the conversion tool. Secondly, you can hard code the converter into your software, however I am not refreshed with the logistics of using this method, so you will need to do some research on such a topic.
Cheers,
Swifty