The tool probably shut itself off after getting multiple errors, we made it stop itself after 15 consecutive errors to keep your account safe, the next time this happens check in your Dashboard == Summary and see if you are getting errors related to the messaging feature.
If not, send a message to support and they will look more into it.
You can extract users and send messages to them without waiting for them to be your new followers, here's a step by step guide on how to do that:
1- Go to TOOLS and then click on your Twitter account.
2- Go to Contact Tab
3- All you need to do here is enter the url of an account you want to extract its followers and press start and wait for Mass Planner to get all the followers.
4- Go to Use members tab, and select all the members you want to send a message to.
5- Scroll down, write you message. Make sure if you send a message you send a very good one that doesn’t look like spam so you have a better chance of it being read, you can use spin syntax in the field however that’s only in case you send too many messages so Twitter doesn’t see it as spam.
If you don't have that extra module, you will need to buy it first