Diagnosis
That's the high-temperature protection error. Yeah, this one's common. The unit's internal sensor thinks it's getting too hot, usually because the exhaust isn't venting properly.
How to Fix It
First, power the unit off completely. Go check your window vent kit—make sure the exhaust hose is fully connected to both the back of the unit and the window adapter, and that it's as straight as possible without any major kinks or sags. The window seal should be tight. Clear anything blocking the air intake or exhaust grilles on the unit itself. Let it sit off for 10 minutes, then turn it back on.
If That Didn't Work
The issue might be inside. The condenser coil could be caked with dust, causing it to overheat. You'll need to open the rear panel (unplug it first, obviously) and gently vacuum the coil fins. Don't bend them.
Heads Up
These units generate a lot of heat out the back. If you're using it in a tiny, cramped closet of a room with no other airflow, it can basically choke on its own hot air and trip E1 even with a perfect setup.