Hello Toni,
Thank you for contacting us.
This error is happening when you try to add one of our item templates (you've experienced it with the RadForm item template) to a solution folder. It's a known bug in our Visual Studio extensions which is fixed and will be released in a few days, when we upload the latest version of the Visual Studio extensions to the Visual Studio Gallery.
Please do not hesitate to contact us if you have any other questions or feedback.
Regards,
Momchil
Telerik
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