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I'm coding a VB.NET application on Visual Studio Community. I've created a custom control called an ErrorTextBox, and it basically inherits the TextBox methods and adds in a couple of extra String properties. That's it.

When I'm designing a my ErrorTextBox appears as a custom control in my Toolbox, and I can use it like any other TextBox with my additional properties.

Today, I booted up Visual Studio to continue programming, and suddenly my ErrorTextBox is no longer in the Toolbox. I can't even open the designer page for it. I get these errors:

enter image description here

Can anyone help me understand what's going on here?

Wakka02
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  • Could be alot of things. How did you open the project? Did you use "Open Web Site"? If this is indeed a web application (not web site type project) you should open it with "Open Project/Solution" and find the .sln-file to open it. Hmm though I forgot to ask if this is Asp.Net of Winforms in the first place? – Esko Aug 29 '18 at 11:29
  • Your image indicates that this is a WinForm project; please add that tag to your question. Also tell us whether or not `ErrorTextBox` is defined in the current project. This is a common issue when it is in the same project. When you first create a custom control, you need to do a build before you can place the control on a `Form`. This is because designer needs to load the control from a valid assembly file. If you do something that prevents the build from succeeding, there may be no valid assembly from which to load the control. – TnTinMn Aug 29 '18 at 13:20
  • Possible duplicate of [Could not find type 'xxx.xxx.xxx'. Please make sure that the assembly](https://stackoverflow.com/questions/19009386/could-not-find-type-xxx-xxx-xxx-please-make-sure-that-the-assembly) – TnTinMn Aug 29 '18 at 13:27

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