Well I had no issues to upgrade to 4.2 and I'm on stable 4.2.4
But what I was trying to tell you are.
It's not 4.2 that the issue, it's your OLD database that's the issue and have problems.
I would suggest restoring back to 4.1 then fix the database BEFORE you upgrade.
I don't know how you normally upgrade, but always take defensive steps like disable all 3rd party plugins, applications and themes.
Restore to default IPS theme before attempting an upgrade, did you do this?