I was attempting to replicate the Project tracking video and newsletter. Everything worked fine until I got to the Sequence formula. I cut and pasted the formula into the first cell for the dates. When it executes, I get 00 Jan. There are no January dates in my start or end date cells. Also, it does not save the formula just the resulting value.
I corrected your file up to 6:25 into the video. Note that you had expanded the structured table to include the (dynamic array) header row. You may not use dynamic array functions inside structured tables. That caused the odd header and all the spill errors below it.
Note that the "Gantt" functionality of the colored grid resides outside the structured table. See if you can pick-up the tutorial from here.