Alright! So roughly six months ago I was ripped off by a guy on Craigslist, I bought a 360 from him got it home to find the E74 errors. I eventually just bought a new one, and was out the cash as I could never find the guy again. I was never able to find legit information on the E74 problem beside the fact that it more then likely dealt with the ANA / HANA chip.
After fixing hundreds of 360's now, I thought I'd post my little solution for the E74 problem.
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What you need:
Stuff to open the 360
Basic X-Clamp replacement stuff (follow the other tutorials on how to do this)
Heat gun
Patience
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Ok so here we go:

My workspace

The E74 Error on the current box

Heres the box with the problems

Case off, remove all of the screws, including the little black ones on the RF unit and for the x-clamps

Unplug the SATA and DVD power cables, unplug the fans

Now we have a good look at the chip cuasing all of the problems. Sits directly above the GPU. It's the video scaler chip aka ANA / HANA chip.

And another photo of it

here's a view from the bottom

And another view

Close up of the ANA chip

Here's my el-cheapo heat gun, you can pick up one in the paint section of lowes or home depot.

Heatgun box

Remove the X-clamp from the GPU, take the bolts out of the heatsink

I like the goo gone gel, it works wonders for taking off the stock heatsink goop. Just make sure to clean the area with rubbing alcohol afterward.

Clean the GPU off

Clean the heatsink off

Use the higher percentage rubbing alcohol

Apply artic silver, do the standard X-Clamp fix.

Now the parts we need exposed (underneath the stock x-clamp) are accessible.

OK, so put your heatgun on a medium setting and start apply heat to the marked areas. KEEP THE GUN MOVING you don't want to burn the parts. This will cuase the solder joints to reball themselves (hopefully). Concentrate on the area linking the GPU and the ANA chip.

The motherboard is going to be HOT. Let it cool down. Put the fans and the fan shroud back in, and test it out.

Woohoo!

Nice.
Now if this doesn't work the first time, don't fret. Keep trying, you may need up the heat on your heat gun or give the board more exposure. After you get the 360 running,
keep the case off for a bit, play a few games and see what happens. Some 360's are worse off then others, and may require you to go through the steps again (if the E74 returns).