Please try and reinstall CS5: http://feedback.photoshop.com/photoshop_family/topics/problems-with-photoshop-cs5-after-in stalling-yosemite-version-10-10-on-imac It appears that the OS updater is corrupting PS CS5 if it was installed prior to updating to Yosemite. Let me know if that fixes it for you.
Courtesy of Jeffrey Tranberry
Thanks CS5 working again…..
Thanks for letting me know! I'd at least like to know if the answers worked. It helps future cases.