I've jailbreaked ATV2 yesterday night, so it's running any latest version of software (4.1.1 as ATV2 fw, beta2 for ATVflash)
I've installed XBMC but since it had issues starting I tried to remove it to reinstall it again. Unfortunately after succesfully removing it won't install anymore. When trying I can see the weel turning with a message that it's installing but after a while it goes black screen and then returns to main menu. And the XBMC menu is not there.
Eventually on maintenance menu I can read it's not installed.