For my day-to-day computing, I login to my mac as a non-Admin user (what Apple calls a “Standard” user). I installed Adobe CS5.5 on my machine whilst logged in as standard (authenticating where necessary). It worked for a while and then stopped.
Anyway…. back to the question and the solution (or at least it worked for me !).
Quit all programs and log-off.
Logon as an Admin user.
Login as normal.
Should work !