mistral mpac30 e4 message is; in the over flow water tray there is a switch that the water tray flicks off. If it is not in there properly and the switch is not turned off the message e4 will appear. it is located in the top back corner of the water overflow compartment. You can see it if you look and can touch it with you finger to see if the e4 message goes off. Then you just have to put the water tray back in properly and it should work fine,