OK, maybe you clarified this in earlier posts but, is it only SUM that cannot start the instance?
Can you manually start it? I'm a windows guy so via the MMC or whatever you use on AIX.
Also, on windows and still with SOLMAN, we have the config tool or admin tool whatever its called now, if you launch that and connect to DB, can it? Maybe the passwords in the secure store is messed up?
But again im a windows guy, not even sure you have that as an option.