Hi,
As per standard SAP practice, you can't mix TIme Ticket (CO11N) & Time Event Confirmation (CO19).
This error you are getting since you must have carried out Time ticket confirmation for same operation. If you need this operation to be confirmed with time event then first cancel time ticket confirmation in CO13 and then try with CO19 to post time event confirmation.
Check & revert in case any issue.
Regards,
Tejas