Can't install photoshop cs6 on brand new iMac - "Media db error: 18"

At my company we recently hired a web designer – given his insistence on using the Adobe software, we decided to give Photoshop a try.

We downloaded a trial version and tried to install it on the brand new iMac (no previous installations of adobe stuff) we just bought for the new desigher, but... it's not even installing!

The installation process halts at around 2% and an error screen appears which gives generic instructions ("restart your computer and retry") and points to a log file where one can read "Media db error: 18".

Of course we tried restarting the computer, cleaning up ~/Library, re-downloading the installer... no good – we then downloaded and run an adobe cleanup utility... still no good.

Some people on the internet report they have the same problem... we found several questions on the matter, but no answer (besides "restart your computer" and other generic stuff that we tried and does not work).

We then called Adobe support (Italian support) and they told us they don't give support for trial versions, like we should sight unseen buy a (pricey!) software we can't even install! .

Can anyone here help?