The Developer Console didn't set the DEVELOPER_LOG trace flag on your user. Having an active trace flag triggers debug logging. You have 260 MB of the maximum 250 MB of debug logs. Before you can edit trace flags, delete some debug logs.

1. In developer console, Select tab "Query Editor" at the bottom of the console.

2. Select check box "Use Tooling API".

3. Execute the below query:

1. SELECT Id FROM ApexLog  

4. Select All Rows. Click the first row and then press Shift button and click last row to select all the rows. Delete all rows using Delete button.