Calendar disappeared entirely

Calendar disappeared entirely

napisao/la Sa Ra -
Broj odgovora: 0

I deleted a course from a course category and it caused the calendar to disappear entirely. In the place of where the calendar used to be is the following error: Can not find data record in database table course. 

I am just a Moodle administrator, not a developer. Can any developers please tell me if this is a major issue or is it easily fixed? I am quite worried.

Any advice? Thanks a million.