on Vista, running today's program as it installs didn't work on my system, so I did a quick search:
Try setting the program to Run As Administrator (right click on the program, Compatibility tab, bottom checkbox).
If that doesn't work, check if you have Nero Vision installed, there's a codec or two that conflict. You might get Error 800015 when you hit Convert, or some window complaining about a debugger. If you do, see the program help on Eltima's website, it tells you to run a couple commands to fix it by unregistering Nero dll's, you MUST RUN these commands in a command shell (cmd.exe) with Admin priviledges.