Audio Midi Setup Problem, swiches back to built-in Options

[charliemak]

hi
hey i got this problem. it just stared recently. everytime i use protools i must reset the audio midi setup from built-in to Mbox. this switch is never easy and often involves rebooting several times. i go to system preferences/sound, select digidesign HW (Mbox) ---quit system preferences---open protools 6.9 on my G4/1.3GHZ / 2 GB SDRAM--- go to the setup menu (in protools) select edit midi studio setup---select audio devices only to find that the only item in the pull down window is built-in. i went to the digidesign site, downloaded core audio 6.9, installed it and still have the same problem. every so often i can select M box but it switches back during the session leaving me with no sound output. can ANYONE help.