Had to wipe the hard drive to install El Capitan. Reinstalled CS5.5 (InDesign) but had to select trial mode as the installer ays "This serial number is not valid for this product."
I originally purchased this as an upgrade from CS2, as I could not install 2 on a new computer. Had this same issue then, because the installer could not find CS2 to upgrade. After providing my original CS2 serial # Adobe issued me a new serial number, which didn't work either. After much time on chat & phone support my current # was issued and worked - but not any more, nor do any of the previous ones!
If it will run in trial mode it should work on this computer. Cannot afford an upgrade!
CS5.5 isn't supported on El Capitan. If you can't afford InDesign CC (Creative Cloud subscription), roll back to a previous Mac OS X version. If you only have a new computer (which won't install older operating systems), InDesign CC is probably your only bet.
However, the 5.5 installed without a hitch and let me finish a newsletter - I just can’t register it because it says the serial# is invalid, so I may be cut off after 30 days. Not gonna mess with the system - the last upgrade cost me 3 tech support calls, 3 hours at one Apple store, and two more at an authorized reseller to get it running again. It is not a new computer - 2009 iMac - but a newer one isn’t in the budget either for an old lady on Social Security! And the subscription-only Creative Cloud is just not worth it!
But thanks for your timely response!