You may be out of luck. CS5.5 is unsupported under Yosemite.
How was ID installed? If migration, uninstall it, run the cleaner tool and then reinstall.
After that, I’m afraid you’re on your own.
Installed it by downloading it from Adobe. Have uninstalled, etc... It worked for two days, then started having this problem.
I'm out of ideas. Sorry, but that's the problem with running on unsupported systems.