Some menu options that could otherwise permanently modify a database are disabled in the default "read-only" databases. The following message indicates that you are working with a "read-only" database.
An attempt to modify the database from any dialog opened from Database menu will generate the following pop-up message indicating that the database is not updatable.
Some other dialogs (like Exceptions) will work only as viewers.
The Calculate All options from the Run menu will also be disabled.
The Calculate and Delete options from the Rail Profile/Next menu will also be disabled.
An attempt to modify distance units will generate the message shown above.
The database must be changed to read-write in order to make changes that will permanently alter the database.