Either a Unix command or an API (Applications Program Interface) used in TTP 6 is the most likely culprit. However Micromat NEVER condones using any version of TTP that has not been thoroughly vetted for the upgrade version of OS X you are running. Update versions are generally okay however.
Yes, that was certainly the case when I read all the discussions on Micromat's site when OS 10.11 initially came out, and also for about 10 days or so after OS 10.11 arrived. They even warned about using the beta versions of TTPro that were being developed/tested for El Capitan compatibility.
After the final version (8.0.3) of TTPro was released, though, I still waited to upgrade, as OS 10.11.1 arrived about 2 weeks later. All has been well since. (The other critical app that was updated for compatibility with OS 10.11 after the release was Onyx, and that of course was another reason why I waited).
From my perspective, it is not wise to try and use an older version of a program with each newer OS, unless it has been clearly demonstrated to be OK. One is just asking for trouble otherwise. About the only apps I've been able to use without upgrades (so far) are Quicken 2007 (works fine for my needs), and a calculator called Magic Number Machine (there are probably some others that I don't use very often which still work fine also, but the two I mentioned are ones I use on just about a daily basis).
