Navision requires traceflag 4616 to be set ON. We have two choices for this:

1. Execute the following SQL-statement.
   DBCC TRACEON (4616,-1)
   This approach will turn the flag on for the current session only, that is, as long as the SQL Server is not restarted. Once the server gets restarted, you will have to run the above query again.
2. Add the startup parameter -T 4616 to the SQL server database service: MSSQLSERVER. The best way to do this is to use the SQL Server Configuration Manager. This solution is rather a permanent one and the flag is set across system/service restarts.

If you try to open a Navision database using Windows authentication, it displays a missing stored procedure xp_ndo_enumusersids error in xp_ndo.dll. To solve this, you will need to copy xp_ndo.dll to C:\Program Files\Microsoft SQL Server\MSSQL.1\MSSQL\Binn (default path) and run the following SQL-script:

USE master
EXEC sp_addextendedproc xp_ndo_enumusergroups, 'C:\Program Files\Microsoft SQL Server\MSSQL.1\MSSQL\Binn\xp_ndo.dll'
GO
GRANT EXECUTE
ON [xp_ndo_enumusergroups]
TO PUBLIC
 
GO
USE master
EXEC sp_addextendedproc xp_ndo_enumusersids, 'C:\Program Files\Microsoft SQL Server\MSSQL.1\MSSQL\Binn\xp_ndo.dll'
GO
GRANT EXECUTE
ON [xp_ndo_enumusersids]
TO PUBLIC
GO

Useful References:

DBCC TRACEON:
http://msdn.microsoft.com/en-us/library/ms187329.aspx

SQL Startup options:
http://msdn.microsoft.com/en-us/library/ms190737.aspx

Adding xp_ndo.dll manually:
http://www.dynamicsnation.com/NAVNavision/Forums/tabid/61/forumid/53/threadid/67/scope/posts/Default.aspx