2.6.8 is ICS based. If you were coming from a previous version of MIUI you had to wipe data and cache before you installed it because it uses the 4.0 framework. You must also be on 2.3.4 to flash it. If you didn't wipe before you tried to update or you were still on 2.3.3 then that is your problem. 2.6.8 is ok but if you are wanting to stay on MIUI check out 2.8.10. [ROM][BETA] MIUI vX.X.XX it's a newer version.
At this point try and get into stock recovery. Push and hold volume down and hold power until "fastboot" appears at the top of your screen. Then push volume down 7 times to highlight "android recovery." Push volume up to select it. Now push volume up and volume down at the same time to access stock recovery. Use the volume keys to navigate and power to select data wipe. If that doesn't work a SBF to 2.3.4 is required.
https://sites.google.com/site/motosb...d-x2-sbf-files Go here to find the 2.3.4 SBF and use RSD Lite.
If you wanna check out all the other ICS roms for the x2 check out the rom sections. All require you to start on 2.3.4 so its really your choice. (Note CM7 is gingerbread and Eclipse requires you to be on 2.3.5 but is still gingerbread based.)