You can't set a password for a database (see the following section) if the database is open in Shared mode. Shared mode lets more than one person work on a database at once on a network.
By default, databases are opened in Shared mode. You can override this, and open a database in Exclusive mode, by selecting the Exclusive check box in the Open dialog box when you open the file.
If you want to set the default to Exclusive mode for all databases you open, follow these steps:
Select Tools Options. The Options dialog box appears.
Click the Advanced tab.
In the Default Open Mode area, click Exclusive.
Why Isn't It Exclusive?
If you are reopening your database after you've set the default for Exclusive (see the ...