You need to install Ms run time script in your module.
Go to Module- tools-Refrence- Go down to the middle of the list and choose(Tick) Ms run time script. Do no run- first time, just save and close it.
When you re-open and try to step over and see if you get this error. If you get the error, that can only be you have not installed it properly. Try it again. The code works as you can see from the result. Let me know.