Topic: How to Fix error 66 - Original Phat
When an Xbox 360 shows an E66 error on screen, it is signaling a general hardware failure. A single red blinking light will be present in section 4 of the ring of light on the front of the console, as shown in the picture. An on-screen message, which depicts the E66 error, will instruct a user to contact Microsoft Customer Support.
An E66 error is known from reports online to indicate a problem with the console's DVD-ROM drive. In particular, this problem can present itself when a DVD-ROM fails to pair with the system due to a mismatch in certain details. For example, a drive being a difference make and model than the console expects (incorrect spoofing during flashing may cause this, as would replacing it would a replacement drive.)