1. Do an update. AIX 5.3 ML03 was current in February 2003, if memory servers me correctly.
2. Do a alt_disk_install so if there is something wrong with the updated AIX you just reboot back to the original version.
3. Are your applications code current, or also an older (perhaps unsupported) version. Talk with your vendor and ask about proper (i.e. supported) levels of AIX and the application.
Use this link to find the AIX 5.3 service bulletins of interest to you (and navigate for AIX 5.2 or AIX 6.1).
http://rootvg.net/component/option,c...rt,0/search,*/