The Alarm 2 means that the E3/E4 thinks that the spindle has moved past one of the travel limits. When the E3/E4 is homed, the firmware sets soft limits for both negative and positive ends of travel for each axis.
There has been a g-code command or a jog move that is asking to go past one of these limits. For example, if you home the E3/E4 then jog up in the positive Z direction, then you will get the Alarm 2 because you are already up as high as you can go. The same is true if you move in the negative direction for X or Y.
Check out this video for additional information: