After installing CS 5.5, I grabbed the media to re-install the previous version of Soundbooth (CS 5), which I use regularly for Duane's World. During the installation, an error message came up stating something like "Unable to continue - close the following applications: AdobeResourceSynchronizer". I searched for a while and did not find any application with such a name but did find the process.
If you run across this issue on a Mac, launch the "Activity Monitor" (it is under /Applications/Utilities/Activity Monitor.app). By default, the activity Monitor will only show Active Processes and you will not see the AdobeResourceSynchronizer. In order to stop it, you have to select "All Processes: (Step 1 below), then highlight the process "AdobeResourceSynchronizer" and then hit Quit Process (Step 3 below).