This happens when you're trying to paste a link to a YouTube video. Since there is no known fix, I recommend re-installing the application and then disable all the background programs. If you have an antivirus installed, then you will either have to disable it completely for the time being or add the software to the exclusion list. Sometimes errors are caused by antivirus programs that block some important modules in applications.
For additional help, check the FAQ page provided by the developer with solutions to known problems: http://www.any-video-converter.com/support/faqs/youtube_faqs.php