i've had this problem before and posted but i don't really remember how i resolved it. no one had the answer then, but i'm hoping someone might now as i've been at this about a week now. i have a new imac 27 to replace my 24 that has a mysterious problem that me nor apple store can figure out. anyway i mounted the 24's drive via EHD enclosure and used migration assistant since then, i keep getting messages from time machine (which i never turned on to begin with) that it could not back up no backup drive has been selected. it will NOT stop. ive comtemplated using app zapper to get rid of it, but may want to use it in the future, so other than that, i'm open to try most any and all suggestion to fix this problem.