This is often an issue when you get a SQL Backup from a customer to analyse.
Off course you can create a user on SQL and change the password, but it is easier.
Navision stores the users into two tables. User and 'Windows Login', The first table is for database logins, the latter for Windows Logins.
When you delete all records from both tables Navision will no longer ask for passwords and allowes blank access.
So to all end users: Protect your backupfiles!
It seems almost impossible to keep up with all blogs. :(
This time I was faster : mibuso.com/.../how-to-get-access-when-you-cant-get-into-your-nav-sql-db :-)