Could not find type 'xxx.xxx.xxx'. Please make sure that the assembly

I believe the issue is that Visual Studio is natively 32bit and one cannot do GUI editing for some components (E.g. ListView) in 64bit. E.g. on forms where you have ListView, you need to change the solution to 32bit to edit the GUI.

So the answer in short is, when you're facing this issue:

1. Change the solution to 32bit or AnyCPU
2. Clean and rebuild the solution/project
3. Open the GUI for editing
4. Save, change the solution back to 64bit
5. Clean and rebuild
6. Run in 64bit

Unfortunately Visual Studio doesn't come in 64bit as yet, hence all controls need to be designed in 32bit mode (or AnyCPU mode).

See this question for more details.

VS 2010 designer error 'Could not find type XYZ' in Windows7. Works fine in XP

I had this problem. It happened only in one form designer view, despite it was able to compile, start, show this form in runtime and show other forms / controls in designer mode.

These steps didn't help:

• Clean & rebuild
• Restart studio
• Deleting all bin and obj directories
• Removing and adding references
• Denial, anger, bargaining, depression, acceptance

Solution for my case:

1. Rename a type, which is missing (for example InformationBox => InformationBox2)
2. Refresh designer (WOW, it works!)
3. Rename the type to its initial name

Change Any CPU to X86. Your control is 32bit trying to run on 64bit machine and cannot find the 64bit version of the control.

I had this same error recently with VB.Net in Visual Studio 2013 working with a custom WinForm User Control that itself was inheriting a custom user control base class in the same project, and took some doing to find out what the true cause was, which in my case was that neither base class nor the child class had a no-parameter constructor (Because that's not a valid scenario in this case).
To fix it, I added the missing constructor but left it empty (throwing a NotImplementedException caused another issue that prevented it from displaying). It's not pretty, but it works.

In order to see the underlying error through the one listed in this threads question, I had to do the following:

1. Clean the entire solution
2. Close Visual Studio
3. Re-open Visual Studio
4. Re-open the solution
5. Build the solution by right-clicking it in Solution Explorer (Not Rebuild, that didn't work)
6. View the User Control in Designer mode and the actual error shows up now

After adding the constructor, I had to take the above steps again to make it work properly.