^ See page 19, post #271 of this thread:
"Make sure you keep fiddling with the ribbon connecting the ssd. I got the red x when installing and ssd into my 7g classic over and over and kept messing with the ribbon cable and finally got it to work flawlessly. It was the super talent 64gb drive so I can't confirm that the 256 will work but I would suggest to kept trying it a few more times."
I do not have an iPod to help right now, but I would google "iPod red X" and see if there is additional fix.
This is from Apple:
http://support.apple.com/kb/TS1463
Symptoms
You may experience an issue on your iPod where the iPod will show a red "X" icon on the display as shown below:

Resolution
- Disconnect iPod from your computer.
- Manually put iPod into Disk Mode.
- Open the latest version of iTunes and connect iPod.
- Restore iPod.
Another answer:
1. Try a reset. Press and hold the menu and the center buttons together until you see an apple logo.
2. If that does not work, Press and hold the menu and the center buttons together until you see an apple logo. The very moment you see the apple, press and hold the center button and the bottom button (play/pause) together for 10-15 sec. You may get a disc mode message on your ipod screen.
Now connect it to the computer, open itunes and try to restore the ipod. If that too does not work, the ipod has to be repaired/replaced, unfortunately.
For an iPod with HDD, people actually hit it hard on its side to get it to work (but I do not think this is the way to go for a SSD iPod):
http://www.fixya.com/support/t605515-red_x_icon_ipod
Edited by zzffnn - 9/10/12 at 3:05pm