I just changed from a Windows machine to a Mac OS X El Capitan. After this I'm having big problems with the program shutting down unexpectedly when linking in pictures from a server, or from an external hardisk. Sometimes it works, and some times it crashes. It does not matter if its linking from a Mac configured hardisk, the server on the intranet or a windows hardisk. It crashes just as often.
Hope someone can help me on this.
CS6 is unsupported on El Capitan. It might run, or might not, you are on your own. You will have to Upgrade to a CC subscription.
CS6 is also included in the CC subscription. That version is slightly different to the version you have from the Creative Suite. It shares components from the CC and will probably run. If you need CS6 to be compatible with coworkers you can use the CS6 from the subscription. (And of course you can use CC, CC 2014, CC 2015 and soon CC 2016.)
As Willi points out, CS6 is unsupported under El Capitan. This forum is absolutely littered with others that have moved to 10.11 and have experienced all kinds of issues.
Roll back to an earlier O/S, upgrade to Creative Cloud or learn to live with it. CS6 has reached EOL and will never be updated again.