This is usually caused by a conflict with another plugin.
The best way to figure out if this is the case would be to disable all of your plugins other than Contest Burner. If Contest Burner starts working and you can create a contest then you know there is a conflict.
If it starts working then you can reactivate your plugins one by one and if at any point Contest Burner stops working then you know the last one activated caused the conflict.
If you leave that plugin deactivated then you should be able to use Contest Burner without any trouble.

If you are still unable to add a contest after turning off all other plugins then another possibility is that your MySQL database on your site might be running in strict mode which causes a problem with Contest Burner. We are currently working on this problem and hope to have this fixed in a future update.

To disable Strict mode you will need to edit the my.ini or my.cnf file depending on your operating system.

You can find further documentation on this on the here:

http://dev.mysql.com/doc/refman/5.7/en/sql-mode.html