I just updated our MPX G2 Diagnostics page to include information about the power up diagnostics.http://www.stecrecords.com/?RecordId=378&search_string=mpx%20g2
To summarize, E1 is pretty bad. Technically, it means that the main host processor self-test failed. Bad, bad, bad. Good news is, it's very unlikely that the z80 is actually faulty. The vast majority of failures on these kinds of products is bad connections and power supplies.
The most likely "bad connection" for a G2 with a diagnostics problem is the FLASH ROM chip seating in its socket (I'm pretty sure it's the only chip in a socket but it should also have a label on it with the firmware version). Sometimes they work themselves out due to vibrations. It's worth putting a dab of silicon rubber on the ends of the ROM to prevent this from happening (if you do this, easy-does-it. Remember, you may need to pull that chip out again someday so don't over do it).
A few questions:
Is the unit otherwise dead? LEDs, LCD, etc..
Does it do anything if you press any buttons?
Does it fail every time or is it intermittent?