Hi @haha yes ,
Welcome to Microsoft Q&A!
Which version of Visual Studio are you using? What is the target framework of your Windows Forms project?
Please update your Visual Studio to the latest version.
Then, launch your VS and create a new Windows Forms project.
Before renaming the form, please close all tabs in code editor.
Trying to rename again and check if the error disappears or not.
Sincerely,
Anna
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