There are two possibilities.
First, you may have more than one AM* device in your system. If they are not correctly set for the master/slave configuration (example, two units both set as masters), then all the LED's will come on. Check to make certain the master is the first unit in the chain (there will be no cable in the expansion out jack on the back panel). ALso make certain that all the slaves have the master slave switch set to the slave position.
The second possibility is that you have all the channels set to direct mode - on all the time. Double check the dip swithc on the back panel for each channel. If you want automixing for that channel, set the correct DIP in the auto position. There is a graphic on the back panel showing the dip switch settings.