If you do a forum search, you'll find a whole bunch of reports of all kinds of bugs in Yosemite.
The answer to most of those have been to downgrade to a more stable version of the OS until Apple fixes the bugs. Nothing Adobe can do about that.
Note: I do not work for Adobe. These are user forums.
Adobe recommends a CS5 reinstall because the Yosemite upgrade does damage the CS5 install. Hopefully it should run after that.
See this topic if you are not sure.
I’m going to try & reinstall the software shorty. I’ll post on the outcome. Hopefully that resolves the issue. Upset with myself as I know better than upgrading operating systems when there first released. Always best to wait a few months till the issues have been worked out!