Dunno what is happening here. The WIP builds, of course, have fixed the lockup on an invalid version of WMV.... but the first thing to test when things lock up is the images used.
Like Yuyu said, 99% of the time it's the vid.
"o" is getting close, though.... within a few more days, the plug-and-play stuff will hopefully be progressed to the point that significant work can be done by the WIP ActionScripters. I don't plan on putting much more "flash" into MXM - I expect an update to "o" within a few weeks to clean up any issues that arise from the public release.
That said, with the UI complete enough for serious scripts, work to a public release should go quickly.