Dear Ewern,
Thank you for your question.
As described in below FAQ:
http://www.solveigmm.com/forum/index.php?topic=2332.msg5925#msg5925
This message caused by an absence of DIVX or whatever decoder on your PC. If you download and install it, preview should get started to work.
You can download the necessary codec at the link below:
http://www.free-codecs.com/download/FFDShow.htm