popVideo Converter 2 will use the video codecs you have installed on your computer. So if you have recently moved from Windows 7 to Windows 8 all your video codecs you used to have are no longer there, which is likely why you are now encountering problems.
You just need to ensure you have suitable set of codecs installed in Windows 8 and you should have no problems. I'm using Windows 8 without any issues with popVideo Converter.
I will say it is almost essential you also have a good quality video converter such as the free Format Factory because there will always be some video formats not supported by PC2 that will need converting.
For me I use DivX or Xvid for AVI, WMV works almost perfectly straight out of the box, and if you want to use MOV format then you will need to install the latest QuickTime software.
I hope this helps.
Peter
Forum Administrator
www.reallusion.com