Logshipping alert emails are being sent out while there is no error

I have logshipping setup with a Primary and a Secondary, and this has been working fine for a long time. Yesterday I started reveiving these emails:

The log shipping primary database SERVER.DATABSE has backup threshold
of 300 minutes and has not performed a backup log operation for 2670
minutes. Check agent log and logshipping monitor information.

Checking the server I see backups being made, copied and restored. All in good order.

Executing execute sp_help_log_shipping_primary_database @database = 'DATABASE'
shows me the last backup date is ‘2012-10-16 07:00:00.673’ as expected.

Things I have tried:

execute sp_refresh_log_shipping_monitor
    @agent_id = '43C13441-6892-4C1E-8435-60F4900E5994',
        @agent_type = 0,
    @database = 'DATABASE',
    @mode = 1

EXEC msdb.dbo.sp_processlogshippingmonitorprimary @mode = 1
,@primary_id = '43C13441-6892-4C1E-8435-60F4900E5994'
, @primary_server = 'SERVER'
, @monitor_server = NULL
, @monitor_server_security_mode = 1
, @primary_database = 'DATABASE'
, @backup_threshold = 30000
, @threshold_alert = 14420
, @threshold_alert_enabled = 0
, @history_retention_period = 5760 

I have tried to disable the alert:

exec sp_change_log_shipping_primary_database 
    @database = 'DATABASE'
    , @threshold_alert_enabled = '0'    
    ,@backup_threshold = 30000

And I have disabled the SQL server agent job ‘LSAlert_SERVER’ which sends out these emails. Even so, emails get sent put every 10 minutes.

Is there an option I missed?

I have had similar issues to this and every time it was caused by a cloned machine where the SQL components had not been renamed (@@SERVERNAME, Database Mail SMTP, and so on). I would check that possibility first. If the LSAlert job is stopped you should not be receiving mails any more.