Error: 18452 Login failed for user ‘null‘, …

          “Null” or ‘’ means that client windows token is not trusted

          Kerberos authentication is not available, fallback to NTLM (not in a domain, SPN not registered)

          Solution: Create the same account, password on the SQL Server

          Delegation may be required (at least one hop exists)

          Solution: use SQL Authentication or enable delegation

          SQL Server service account cannot query domain

 

Error: 18456 Login failed for user ‘name‘

          ‘Name’ means that principal is recognized, but not authorized to connect

          “Login Failed for user 'NT Authority\ANONYMOUS' LOGON“

          Reason: client is running under LocalSystem connects using NTLM

          Solution: Create a dedicated account on both machines

          “Login failed for user '<domain>\<machinename>$' “

          Reason: client is LocalSystem or NetworkService

          Solution: create login in SQL Server for client machine

          “Login failed for user ‘machinename\User’“

          Reason: client is local user and has no access

          Solution: create login in SQL Server for ‘machinename\User’

          “Login failed for user ‘user’“ (no “\”)

          Reason: SQL Login cannot connect

          Solution: Enable mixed mode

          Note that ‘user’ can be ‘null’ if client windows machine is not trusted, i.e. even SQL authentication requires cross-NTbox windows authentication

          SQL authentication can often be used as universal or the last resort solution to all these problems

 

Error: 18456, Severity: 14, State: XX.

          Client is recognized, but not authenticated

          State: XX is not reported back to the client

          Written into ERRORLOG

 

State

Reason

1

Generic error

2

Login for remote login doesn’t exist in the server

3,4

Failed to decrypt encrypted in-memory password

5

SQL login doesn’t exist in the server

6

Connecting SQL login has mismatched login type catalog

7

Login disabled

8

Password does not match

9

Password is invalid (when changing password at logon)

10

Account policy validation failed

11

Windows login is not authorized to connect

12

Sql login is not authorized to connect

13

Server has paused, no logins are allowed

14

Login cannot be used with this type of connection interface

15

Database specified in the connection string is invalid

16

Default database is invalid

17

Default language is invalid

18

Password cannot be changed for this type of login

19

Failed to decrypt encrypted in-memory new password

 

see also blogs.msdn.com/sql_protocols/archive/2006/12/02/understanding-kerberos-and-ntlm-authentication-in-sql-server-connections.aspx