If you happen to receive a Diagnostic Error, please follow the below steps:
Make sure all other users have exited the database.
Click on File, Maintenance, Database, Maintenance.
You may say Yes to do the backup and save it to your backup location.
Once the backup is complete, click Ok and this will bring up the Database Maintenance Wizard.
Click Next and Next as you will be selecting the default database as this is the one you are currently in and need to compact. Tick Compact Database and then Next. Once the database has finished compacting Finish and then log in.
Note: When searching in the Help Centre, you can put in the exact Diagnostic Error in the search bar, please check these for another alternative
If running the Compact Database or selecting the exact diagnostic error does not fix your error, please raise a case online