CS5.5 is definitely not compatible with El Capitan (10.11). It's end-of-life and will never be updated.
You'd best roll back to an earlier Mac OS X version or upgrade to Creative Cloud software.
Thanks, Steve ....as I noted, I am subscribed to Creative Cloud for Illustrator. As a semi-retired freelancer, it is hard to justify the whole suite. The amount of work I get will not pay for the upgrade. This problem also exists with the upgraded Illustrator.
This is frustrating because I have been a loyal Adobe user since the 1980s, and the cost is becoming prohibitive. The new features/gadgets are superfluous for many of us professionals, but I understand the need for a constant revenue stream. It would be helpful if Adobe would offer "pared down" versions at a lower cost for users with no need for exotic effects. Also, I believe it would be profitable for Adobe since it would attract more users with simpler needs, and present a shorter learning curve for new users.
Might have to roll back to Yosemite .......