Weirdness!
Using Vegas 7.0e (build 216)
Using Quicktime movies (.MOV) as source (don't ask why!)
Using "Playback Rate" in Event Properties to speed some clips up to 4.0
Clip plays fine in the timeline.
Render as .AVI - result is a black screen for the speeded-up clips.

Have troubleshooted (troubleshot?) by starting a new project, importing a random QT .MOV file, changing playback rate to 4, then rendering. If I delete the event from the timeline and add a random .AVI file, speed up to 4.0 and render, it's fine. Random QT files render black, random AVIs render fine.
I assume the problem lies in Vegas' handling of QT movies.
Quicktime version is 7.1.3

Does anyone have any experience of this happening, and/or are there any suggestions for fixing?

Update:
Didn't find the cause, but worked around by using Vegas to convert QT to AVI, then importing the AVI versions of the clips into the project, speeding the clips up and we're good.

Reg, I just tried this your way as well as the Ctrl-drag method and they both worked for me.
Vegas 7.0e (build 216).

edit: using Quicktime 7.2

My guess is that the files in question use a codec that doesn't take kindly to the access patterns that come from speeding up video in Vegas.

How large are the files?

Do you still have them?

Does the same thing happen in Vegas 8?

What version of Quicktime are you using?

Thanks,
Matt