mg1312, I do not know what codecs you have installed but if you have not used it I would recommened the K_Lite Mega Codec Pack which you can download here:
http://www.free-codecs.com/download_...hp?d=2188&s=42
It covers almost every codec you could think of. If you are still having problems then you may need to convert the file to .AVI before converting to SMV