thanks for reporting TaskChain issues here on the HotPot forum
Please enable Moodle debugging and let me know on what line number of what script the error occurs. Also, please copy and paste the URL of the page on which you saw the error. You can skip the domain name at the beginning of the URL, I just want to to know the latter part, after "/mod/taskchain/..."
Upon further investigation, I believe that this issue was confined to displaying the columns for "Entry page" or "Exit page" on the "Edit chains" page, when one of the TaskChain activities specifies a particular activity by name as either the "Next activity" or "Previous activity".
The URL of the page was something like ...
The issue is fixed in the latest release of the TaskChain which I have just made available via github.com and moodle.org.
Please upgrade the TaskChain module on your Moodle site at the next convenient opportunity.Thanks for bringing this issue to my attention