hmmm ... should not happen ... but maybe you can try atadisk.dll ?
if you have some regedit tool for the 720, try looking into HKLM->software->drivers->built-in or something ... there is one that is something like that ...
or you can look under \Windows and see if its atadisk.dll or something. I don't have my MP790 with me right now to check. Someone help here.