Breaking Log Sequence Number(LSN) Chain

Sometimes, the LSN of the log is broken due to some user actions. This could be very vital mistake as you cannot take the successive log backups until a full or differential backup is taken and in case, if you have to take tail log backup, it is not possible which means you are going to have some data loss.
The actions that could cause this are switching the recovery modes or taking log backups with options such as Truncate only, no_log.
If the LSN chain is broken, it potentially invalidates the log backups thereafter.
You will receive this message when log backups are invalidated.

The things that can cause this are:
1. Switching the Recovery modes.
2. Taking log backup with Truncate only option.(This option is not present SQL versions 2008 and above).
3. Taking Log Backup with No_Log option.(This option is not present SQL versions 2008 and above).
4. Reverting the database from Database Snapshot. This requires full backup of the database, differential backup will not fix it.

To fix this, either take a full backup or Differential backup and then continue taking log backup.

1. Switching the Recovery modes
create database Test1
Backup database Test1 to Disk = 'E:\Backups\Test1.bak'
Alter database Test1 set Recovery Simple
Alter database Test1 set Recovery Full
Backup Log Test1 to disk = 'E:\Backups\Test1_Log.bak' --- Error here
Drop Database Test1
—————————————————————–
2. Taking log backup with Truncate only option.(This option is not present SQL versions 2008 and above).
create database Test1
Backup database Test1 to Disk = 'E:\Backups\Test1.bak'
Backup Log Test1 to disk = 'E:\Backups\Test1_Log.bak' with truncate_only
Backup Log Test1 to disk = 'E:\Backups\Test1_Log2.bak' --- Error here
Drop Database Test1
————————————————————————————–
3. Taking Log Backup with No_Log option.(This option is not present SQL versions 2008 and above).
create database Test1
Backup database Test1 to Disk = 'E:\Backups\Test1.bak'
Backup Log Test1 to disk = 'E:\Backups\Test1_Log.bak' with No_log
Backup Log Test1 to disk = 'E:\Backups\Test1_Log2.bak' --- Error here
Drop Database Test1
—————————————————————————————–
4. Reverting the database from Database Snapshot. To fix this, we should take Full Backup. Differential Backup will not fix this.
create database Test1
CREATE DATABASE Test1_Snapshot ON
( NAME = Test1, FILENAME =
'E:\Backups\Test1_Snapshot.ss' )
AS SNAPSHOT OF Test1;
GO
Backup database Test1 to Disk = 'E:\Backups\Test1.bak'
Restore Database TEST1 from Database_SnapShot = 'Test1_Snapshot';
GO
Backup Log Test1 to disk = 'E:\Backups\Test1_Log2.bak' --- Error here
Drop Database Test1_Snapshot
Drop Database Test1

Also, you will get this error if you have not taken Full backup prior to taking Log backup. In such case, take Full Backup.