The error "object reference not set to instance of an object" typically occurs when you are trying to access an object that is null or has not been initialized. It's hard to say exactly what the issue is without more information on the specific code and project, but some things you can try include:
- Check that all objects being accessed in the form's design have been properly initialized.
- Clean and rebuild the solution to ensure that all dependencies are up to date.
- Make sure that the form is being loaded correctly, and that the necessary resources are being loaded.
- Try to open the form in the designer in safe mode. You can do this by right-clicking the form in Solution Explorer and selecting "View Designer" while holding the Ctrl key. This will open the designer in safe mode and may reveal any issues with the form's design.