Invalid License http://helpx.adobe.com/creative-suite/kb/error-serial-number-valid-product.html
-http://helpx.adobe.com/creative-suite/kb/invalid-serial-number-cs4.html
-and http://forums.adobe.com/thread/1038761
IF Mac El Capitan read below
CS6 and earlier programs have not been tested and will not be updated to run on Mac El Capitan
-which means that you try to use CS6 and earlier at YOUR risk of having problems
-you may get CS6 and earlier programs to install and run, or you may not (some do, some don't)
-IF not, post details of any error messages and someone may be able to help
That MAY be a false error message due to Mac El Capitan and OLD programs
This information is a MUST DO to install old programs on Mac El Capitan
-you may not get the same error message, but these are some links that MAY help with old programs
-Java https://helpx.adobe.com/dreamweaver/kb/dreamweaver-java-se-6-runtime.html may help
Install CS5 on Mac 10.11 https://forums.adobe.com/thread/2003455 may help (also for other than CS5)
-also a TEMPORARY security change https://forums.adobe.com/thread/2039319
-http://mac-how-to.wonderhowto.com/how-to/open-third-party-apps-from-unidentified-developers-mac-os-x-0158095/
-and more on gatekeeper https://support.apple.com/en-au/HT202491