Microsoft Access mde file was corrupted. Started receiving the "missing MSysDb" error. Could not use Microsoft Access database tool "Compact and Repair", but received same error. The same happened when trying to export in order to import to a new file.
Used "Access Repair Toolbox" to repair the file. Afterwards, started receiving the error messages "Record(s) cannot be read; no read permission on 'MSysObjects'." and then "Record(s) cannot be read; no read permission on 'MSysACEs'."
Cannot view mde file in Microsoft Access after receiving these errors.
Have read the other answers to issues with the "missing MSysDb" error, but the recommendations did not work. Unfortunately, the file was not backed up.