ok, here's the deal...

created a preject in v7
rendered out uncompressed .avi (with alpha channel)
tried to open my newly created file in a new project
vegas gives me an "unsupported format" error.

had no problems opening pre-v7 avis or .mov with alpha channel.
i even reopened the original project, & was able to open it there (the new .avi). any ideas?

edit: figured it out. audio settings were different. one project was 5.1 surround the other was stereo.