"request parameter validation failed" error

“request parameter validation failed” error when updating Calendar (gmail)
Started a few day ago.  Haven’t made any changes to my email client or to gmail.
Ver: 6.0.24928


Can you please check your google account security settings if “allow less secure app” is enabled?


I just enabled 2-Step Verification and apparently can’t view or change this setting.

I have removed my 2-step verification, and allowed less secure app’s.  But, I’m worried that it will synch and call up the less complete gmail calendar info.  How do I retrieve my previous calendar entries that weren’t in gmail calendar? 

Does anyone have any advice on this?  Should I close the app and see if the calendar entries return?  Where did they go?