Sorry to bear bad news but the E20 code is a dead laser. I had it two years ago and had to buy a new head unit. I'm much happier now with a Kenwood that plays MP3's and has more amp power than the stocker. Oh, it cost about $275 to fix the factory unit if you want to go that way.
Time to

i had the same problem. my cd player showed the same error message. the pontiac dealer did a swap for a reconditioned unit for about $300. this left me with steering wheel controls that still work, and it still looks like it belongs there as opposed to an after marketunit.

2000 gtp daytona
3.4 pulley, cold air box, tb spacer,over size wp pulley, tog headers, r/t down pipe and high flow cat, resonator removed and replaced with 3" pipe.

I'll sell my factory to anyone interested for well under $200. Might have to put it on ebay soon.