Error message while i try to schedule a non-repeating event

This is the first time i have this error pop up when I am trying to schedule a non repeating event for a subject.
This is the error that pops up:

"This type of event may not be added to the specified subject, since the event definition is not repeating, and an event of this type already exists for the specified subject."

There is no such event that already exists for this subject so don't understand why is it giving me this error ?
Attaching a pic of the error. Please advice what I need to do to fix this issue.
Sign In or Register to comment.