[RESOLVED] Framework errors for third party controls

Hi all O7.
I was using licensed iocomp old-fashioned instrumentation controls/activex recently. Since I migrated to VS2019 now on for a couple of months, I pursue its instructions to install like before and they're added to VS toolbox but when adding to form then building a simple WinForm test for any controls of its collection following errors will occur:

- Type 'Iocomp.Classes.ColorSection' is not defined.
- Reference required to assembly 'Iocomp.Instrumentation.WF40.Common, Version=5.0.2.1636, Culture=neutral, PublicKeyToken=a217a64fde564c89' containing the type 'ControlBase'. Add one to your project.

What I've tried:
- Increasing/Decreasing compile .NET Framework version to min/max from 2.0, 3.0 to 4.8 then rebuild = More errors. (Mostly Unable to resolve type 'Iocomp.Instrumentation.Professional.SlidingScale, Iocomp.Instrumentation.WF40.Pro, Version=5.0.2.1638, Culture=neutral, PublicKeyToken=a217a64fde564c89')
- Manually adding its *.dll (5 files) in toolbox "choose item".

What should I do? Kinda crucial. I cannot afford Syncfusion or DevExpress control collections.

Have you added a reference to the library specified in the error message? You don;t add DLLs to the Toolbox. You reference a DLL on the References page of the project properties. The error message says:

Quote:

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Reference required to assembly 'Iocomp.Instrumentation.WF40.Common

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so add a reference to that assembly. If you think you have, please show us a screenshot of your References page.

Oh indeed. I added them to references tab of project and it is now working properly. Sometimes I feel embarrassed.

Since this thread is resolved let's find something out. "Remove unused references" button is no longer available in this tab. To reduce final product size, to achieve a proper less-possible-errors in run time and to be an efficient and fast starting time winform, it should be perform once before building. Manually try-fail may cause you troubles.

What are your approaches?