It looks very similar to Snmavronis' issue, but the correction I programmed won't work in this case because the file chooser used in the advanced video rendering plug-in is programmed here to select a folder (hint: there's an error in [font=courier new]DirectoryChooser[/font]), and I didn't make corrections for that case.
I'm not sure why Enkonyito programmed this dialog box but requesting a folder shouldn't fail anyway. Let's try first to understand how it really happens in your case. The strange thing is that it works the first time. Do you select a folder different from the proposed one the first time you generate a video? If yes, what files does this folder contain and does it still bug the second time if you don't change the proposed folder?