The number one message I receive is from QuickTime: "Additional software is required for QuickTime to play back this media. It may be available from the QuickTime Components page. Make sure your internet network connection is active, then click the Continue button to check for the software."

Is your LW properly connected (all green/blue connection bars)?
I don't see any green/blue connection bars.
Often I get this message: "The movie could not be opened - An invalid public movie atom was found in the movie".

I registered at BITZI but what is it all about? I'm not as advanced as you are in these matters.

If you'd just said that in the beginning then you might've been able to get appropriate help faster
You said that you had problems with uploads & downloads... not problems with playing already downloaded files.

If you have other ideas besides a helpful Lord of the Ring's now that you see the specific error message, do share.