OK - I narrowed it down to the End Date field. I'm only getting the error when it is left blank. (As it often will be.)
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '','22:00','test','Final_2015_QQ_events.pdf','Event','510')' at line 1
SQL: INSERT INTO `Events` (`Event`,`Summary`,`Heading`,`Details`,`Start_Date`,`Start_Time`,`End_Date`,`End_Time`,`Booking`,`Booking_Form`,`Type`,`EventVenueID`) VALUES ('test','test','test','test','2015-01-14 00:00:00','20:00',NULL','22:00','test','Final_2015_QQ_events.pdf','Event','510')
I can't see what is different about the End_Date compared to the Start_Date. But as the Start_Date is required, I changed it to not be required to check if that errors (i.e. there's an issue with both date fields), but it was fine - so is only the End_Date field causing the error.
I have also checked they are the same format in the database, which they are. (Type: Date. Default NULL.)