Hi KelThuPsyCh05,

Unfortunately I am unable to reproduce the issue on my side. I search this on the net, and found the same error. I guess this may cause by the name of namespace. The error text seems to tell there is something hided and could be accessed. Please check all the namespace names in the files are the same or add using namespace statement, then close the form and reload it. Does it apply to your situation?

This threadis for your reference.

If you have any questions, please feel free to ask.

Best regards,
Ling

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Make sure the Build ActioninProperties for thefile is set to Compile. It's probably set to None.

This is usually caused by having two objects with the same name.

Example:

You have a folder named IOFunctions and you also have a file called IOFunctions.cs somewhere in the build. Make sure you naming conventions are not over lapping folder names and file names.

I had this issue. For me, the issue was that I had a namespace that was invalid. I had added a folder to the project that I then added more folders to represent certain utilities in the project. When creating controls in the sub folders, it was adding the 'Utilities' namespace to the control namespace. However, since I did not actually have any files in the 'Utilities' folder, this part of the namespace did not exist. Once I removed the 'Utilities' portion the control opened just fine.