OM12 SP1 Upgrade: Beware For The Corrupt ISO!!!

Bumped into this issue at a customers location.

The issue
A fairly new OM12 RTM UR#3 environment in place, two OM12 Management Servers and one dedicated SQL Server. All by the book. So time for an upgrade to SP1 for OM12.

However it went totally wrong. On the first OM12 Management Server the installer died on me:

The cause???
The log told me this: ~\Setup\AMD64\Server\OMServer.msi returned error 1603.

I checked this posting written by Tim McFadden, but that issue wasn’t at play here. Went trough the log file over and over but only this error stood out. So not much to go on.

The ISO file I used was the same one I already used to upgrade about 4 OM12 RTM environments, all without a problem. Time for a second trial. But the same error! Time for another approach.

The solution
Since it really bothered me I checked everything over and over only to conclude all was fine with the OM12 RTM servers to be upgraded. But somehow, somewhere the installation kept on failing on me.

The only thing I could think of was to download the SP1 bits again from TechNet and run it from the new bits. Even though the ISO file which was causing issues had been used 4 times already without any issues at all. But sometimes the most obvious is too easy overlooked..

And now everything with the new ISO file went fine! Without a glitch! The upgrade ran like clock work:

Recap
Whenever an upgrade fails and the cause is really puzzling, just download the SP1 bits again and run the SP1 upgrade from those new bits. Changes are you’re in good shape now.

REMINDER
Always make backups and snapshots before performing an upgrade. This time it was really a life savior for me.