This happens to me as well on boost I was reading that the android market updated their servers to give android users a more rich experience and to boost sales on market. This is why you now see apps like google maps, and gmail, and youtube, and skype and on and on. they let you download them but not install. I also read that this is an issue with the i1's software. Just another reason there needs to be an os update or a maintenance update something.
believe me when I tell you your not the only one. Motorola is supposedly looking into it. Lets hope the issue gets resolved quickly.