Toast will only accept files that can be played back in QuickTime movie player. If the cannot be played back, it's more than likely it was created with an encoder/decoder (codec) that is not available on your computer.
Any one format, like .avi for example, can have numerous versions created by anybody from DivX to video camera manufacturers, to hobbyists trying to make a better compressed video. In other words, if you don't know how the file was created and the codec to decode it, it won't play.
To import your file you will need to do the following:
Determine what codec created the file and install it on your Macintosh. Once the appropriate codec has been installed on your Mac and QuickTime, it will work fine in Toast.
To help, Apple offers a large list of available codecs (most of them free) for QuickTime that maybe able to read your file (Video or Audio). The most commonly used codec for importing video files is Perian.
Note: Roxio has not tested these codecs with Toast and cannot guarantee that they will resolve your issue, maintain system stability, or any free "shareware" status.
If you cannot find a compatible codec from the above links, then it maybe a newer codec that hasn't been written for the Mac OS yet.
If the file came from a camera, the camera manufacturer most likely included software to convert the files to other formats. Install this software and convert it preferably to a .mov file or a format that can be be installed from one of the codecs on the Apple site mentioned above.