Can not delete or rename a maintenance plan for exception thrown by mscorlib. How to resolve it?

In some case (most likely after an upgrade), you may face trouble to delete or rename an existing maintenance plan. If you attempt to delete or rename a maintenance plan, SQL Server throws an error as below:

Exception has been thrown by the target of an invocation. (mscorlib)

The connection manager "Local server connection" will not acquire a connection because the package OfflineMode property is TRUE. When the OfflineMode is TRUE, connections cannot be acquired. (Name of the Package you are working with)

This error happens because you have .dll registration related issue on your client tool. So simply use another SQL client installation on another machine to delete or rename maintenance plan.

If you need to permanently fix the problem, then re-registering the dts.dll on the OS. However as this is not an issue with the server component, it is not recommend doing anything on server if you face this issue with the client tool installed on the server itself. (You should not use production server to log in and work on client tool unless absolutely necessary).