Hello Min,

Thank you for posting in our forums.

You need to add a contstructor to your MyFormsManager class which accepts IContainer parameter and calls MyBase.New overload which accepts IContainer:

    Public Sub New(container As IContainer)

        MyBase.New(container)

    End Sub

Then you may need to delete and re-add your MyFormsManager instances in order for the designer to start using this overload.

I have attached a sample demonstrating this suggestion.

Please let me know if you have any additional questions.