I have checked the official website of the developer and couldn't find any information about NetSpeedMonitor and its availability on Windows 10. This means you will have to contact him and provide information about the error. He will either request logs for this error or give you a proper version of the software that works on Windows 10. Use one of the Social services to get in touch with him.
Official page: http://www.floriangilles.com/
Please note that the product appears to be discontinued, and support for the program might not be available.