After installing Adobe Web Premium CS4, I tried to import a video clip that was shot on a little Canon PowerShot camera into Adobe Media Encoder.

It immediately responded with the error:

The file "CIMG1324.AVI" could not be imported."

There were no entries in the log or error log to clarify this this, so I started searching Adobe.com. It turns out that AVI is not a supported file format in Adobe Media Encoder, at least not on the Mac. You must convert them to DV AVI first.

Opening the movie in Quicktime, select File>Export>Movie to DV Stream did the trick, and my files converted beautifully after that.