The error occurs in the planning console when a task is added and saved.
Uncaught TypeError: Cannot read property 'topTask' of null
It looks like the description of the top project was copy/pasted from Word or a different application. Unsupported smart-quote characters are in the description: “”
This is known to cause issues and we suggest against using them in the platform. Instead, use the conventional quotes "", which have not been converted by a third party application.
Please replace the quotes from the description with "" and the project will save properly.