I'll give it a go. In your original example where you pointed us to the link to 0.8.4.0 the example page (when describing YouTube URL) had a longer(?) url than I had in mine. For example when I pointed to a YouTube video, the yellow highlighted section looked like this (just an arbitrary/current video)
http://www.youtube.com/watch?v=jg2bnZwZuGY with the file name filled in.
Whe I pressed the 'youtube' button, it gave the file size after "checking URL" msg.

However, when I pressed OK, I got the "YouTube URL error".

NVC 0.8.4.0 works on file conversion, but I'm not sure what's going on with the URL bit.

Hope that helps?