If you are getting an error message that looks like below and states "Cannot publish the stream. Verify the stream name and if you have provided any credentials/tokens that are up to date" there are two reasons for this.
The first is, if using HTML5 All Device, make sure you are entering the login and password correctly. If you need help, follow this guide.
The second reason is because someone is already streaming to this channel. If you use multiple encoders in different locations, please make sure that one of the other encoders hasn't been left on. This should be easy to confirm because the "offline" message will not appear when you preview the channel content.