WindowsForm designer errors

Hardly. I can guess what happened. 1) The project still compiles, just try it. 2) Before Windows patch, the designer view already wasn't displayed; you just did not pay attention for that. 3) You did not pay attention for that because before this view was not opened. Yes, you did not change the code, but you changed the .suo file, current state of the IDE.

So, to start with, close the designer view and ignore the problem. Try to compile it. Chances are, it will compile and may even work. If it does not compile, we have not enough information to solve you problem.

Now, how to solve the problem?

First, stop doing what you are doing and start doing software development. You will say, "How, what else do you thing we are doing? Software development!" I would not be so sure. I suspect that you are just wasting your time, or, more exactly, risking all your development time. To start software development, you need 1) start using some Revision Control System, 2) implement single-click batch build of all the software. If was was wrong in my assumption and this is all implemented, please forgive me and go to the next item. If I was write, do it immediately. Otherwise, your valuable code asserts are not yours, but they belong to the first slip of a hand or a hardware crash. You need to be able to retrace your steps in all situations.

Now, fix the form. I suggest to assume it was broken (it usually happens indirectly) during development well before you had the Windows patch update (and now you observe the result of usual coincidence, as many people before). Here is what could have happened. There are many aspects of the form (WPF window or other unit developed with the use of designer and/or XAML) which work fine during your application runtime but fail during designer's runtime. This is just the simple fact that different methods you implemented are called in different order and different environment. Your form methods may call some methods from other files, or you modified those methods without showing the design view for a while.

Try the following: enclose as much code of the form methods as you can in the check:

if (!DesignMode) { /* ... */ }

In other words, keep existing functionality, but only execute most code when you are not in the designer. It's very likely that you can load your design view after this "trick". If it cannot help, continue debugging in a usual way. In further development, try to keep all questionable code which may potentially fail away from the form and design mode. Try to isolate UI from all other aspects of programming. This was one of the primary motivation items for MVC, MVA, MVP or MVVM.

Yes, I understand that I assume too much. But you did not provide information to find more specific cause of action. In my experience, most problems like yours circulated around the activities I tried to describe.

—SA