You have most likely removed the _EditEventRule privilege from the application or the Role your username is added to.
Please follow this guide to restore some of the default settings to your application.
1. Login to SiteAdmin
2. Click on application in list
3. Scroll down to "Synchronize"
4. Select "Basic One" in drop down
5. Click on Synchronize
Use Roles and Features/Privileges:
Overview of all common privileges