high!
i've got an error too.. take a look at virtual dub' message, displayed when wmv file tried to be opened:
"Not supported: Microsoft owns US patent #6,041,345 on the ASF file format, preventing third-party applications from extracting data from ASF files. ASF file format support was removed as of V1,3d at the request of Microsoft and to avoid patent infringement claims, and as such VirtualDub no longer supports ASF. Please do not ask for versions that do."
it seems to me the only way to open it in R4 is to reconvert your files with some kind of "power video converter"..