looks like someone restored msdb ? or maybe actually did a DBCC CHECKIDENT with Ressed?

the diagnosis is easy, and so is the fix:

the diagnosis:

use msdb;

GO

DBCC CHECKIDENT ('dbo.backupset')

SELECT MAX(backup_set_id) + 1 FROM dbo.backupset

if the current identity is less than the max row in the table, that explains the error.

the fix would be as follows:

use msdb

GO

Declare @FixedKey int

SELECT @FixedKey = MAX(backup_set_id) + 1 FROM dbo.backupset

print 'new correct key is ' + convert(varchar,@FixedKey)

DBCC CHECKIDENT( 'dbo.backupset',RESEED,@FixedKey)