Unable to Delete SQL Server Maintenance Plan and SQL Server Agent Job

Problem

I have encountered an error recently when I was doing some test to build a maintenance plan in SSMS. I tried to delete a maintenance plan which I did not need any more, an error showed up:

Exception has been thrown by the target of an invocation. (mscorlib)
Additional information:
Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index (mscorlib).

When I tried to delete the SQL Server Agent job related to this maintenance plan, this error showed up:

Drop failed for Job "Database Maintenance.Subplan_1". (Microsoft.SqlServer.Smo)
Additional Information:
An exception occurred while executing a Transact-SQL statement or batch.
(Microsoft.SqlServer.ConnectionInfo)
The DELETE statement conflicted with the REFERENCE constraint "FK_subplan_job_id". The conflict occurred in database "msdb", table "dbo.sysmaintplan_subplans", column 'job_id'.
The statement has been terminated. (Microsoft SQL Server, Error: 547)

Solution

We will have to remove the data entries of the jobs and  plans manually from "msdb" system database.
The following is the steps to be taken:

Step 1. find the job_id for the job

use this query to get the job_id:
use msdb
go
select job_id from sysjobs where name = 'yourjobname'

Replace yourjobname with your SQL Server Agent job name shown in SSMS. In my case, it is 'Database Maintenance.Subplan_1'.

Step 2. find the plan_id

use this query to get the plan_id
use msdb
go
select plan_id from dbo.sysmaintplan_subplans
where job_id ='yourjobid'

Replace 'yourjobid' with the job_id obtained from Step 1.

Step 3. delete the data entries of the jobs and plans

Use these queries to delete the records:
use msdb
go
delete from [dbo].[sysjobschedules] where job_id = 'yourjobid'
go
delete from [dbo].[sysmaintplan_log] where plan_id = 'yourplanid'
go
delete from [dbo].[sysmaintplan_subplans] where job_id = 'yourjobid'
go
delete from sysjobs where job_id = 'yourjobid'

Step 4. delete the maintenance plan package

Connect SSMS to Integrated Service.

The expand "Stored Packages" -- "MSDB" --- "Maintenance Plans", right click on the maintenance plan, and select "Delete" from the right click menu.