Thanks for the tips!
I did not run any anti-virus software, so that couldn't be the problem.
On the other hand - my folder organisation MAY be, but...: Before installing I read very carefully the documentation that follows the suite, here are some quotes:
"On Mac, you cannot install to the root drive."
"Although you can choose to install an edition of Creative Suite 4 on a secondary
partition, the installer still requires up to 6GB of free space available on the primary
partition to complete the installation."
i.e. There was nothing in that text that stated exactly where the apps should be installed, or that it would be crucial to keep them where Adobe put them. And the second quote even implies that I can choose another drive/partition, way out of applications folder...
(I like to be able to sort my apps in my folder, via subfolders. Otherwise the list gets to long and crowded.)
Well, I'll try to move for instance my Photoshop folder back to Applications and see what happens.
Edit after trying: I moved the PS-folder, started PS (which will give you a notice that some things must be repaired since it has detected a move, I klicked OK), quit PS, tried the update twice, didn't work and failed without a message, exactly as before. Buggers.
Do I really have to reinstall my Creative Suite??