Cthulhu

I'm so confused.  I'm a not-very-tech-savvy senior so calculations etc throw me for a loop.  I have a data dump from our timekeeping database. Columns include: Employee, Division, Section, PayGrade, Date, Hours, to name a few. There is 11,000 rows with 200 employees and the dates they worked.  I need to add a column to the dataset or a measure to a table visual to show how many consecutive days they worked (including weekend days) so that I can identify those who worked 7 consecutive days or more (and needs to reset after a 1-day gap).  I watched the video and read whatever I could find. And I'm stumped. I tried to copy the Cthulhu calculation and I got an error.  Any help would be appreciated.   (I've attached the calc pic in PBI with the error and the calc in excel so the bottom of the calc shows)