We’ve fixed the date validation for CSV imports in the Event Calendar app 
Previously, the widget could import a CSV event dated, for example, the year 206, and the import would succeed and add it to the config, but the widget wouldn’t be able to parse that date and would crash, as shown here.
Now, the CSV import process rejects events with dates the widget can’t parse, preventing crashes.
I am getting this error on all my lines even though the D&T format seems correct.
Line 2: Invalid date. Please enter a valid date with a 4-digit year.
Hi there and welcome to the Community, @Noel_O_Connor 
This error occurs in the widget configurator when importing events from CSV, right?
If so, could you please share the name of your Event Calendar where you’re importing these events and send me your CSV file in a personal message?
I’ll ba happy to take a closer look 