Hi,
This is Gary the creator of MCEVideoEncoder. I have not encountered any of these error myself so cannot help without more information.
Please email me (my support email address is on my www.lightningware.co.uk website in the help pages) your problems with more detail and I'll look into them. Once the solutions have been found I will post them back here.
Off the top of my head a class not registered bug will appear if you haven't got one of the required libraries on your PC. Please make sure you have installed Windows Media Player
V10 and Windows Media Encoder
V9 before you install MCEVideoEncoder. You will also need to install any codecs the videos use (use gspot codec app to find this out).
Please remember that this is software in its beta stage and therefore small bugs may crop up. I will try and fix them ASAP if required. Your continued support is much appreciated

.
Hope this helps.
GazzaS