Cos its a MAC and it prefers a QT (.mov). Apple has designed MACs to be very proprietary so they can charge you a lot of $$$ for software and hardware.
You MAC guys never get this and buy into it!!!
hello i also have this issue.
I can import this avi with the yuy2 codec usign premiere pro cs3 in windows but not cs4 on mac.
I use AVIs in PPro Mac all the time, captured in the Windows version of the program. If you can't use a particular AVI on the Mac it's because you don't have the applicable codec installed. Remember that AVI is just a wrapper. Same with MOV files. Also be aware that PPro Mac can be fussy about which AVIs it will accept. Generally speaking, if they weren't captured in the program it probably won't like them. Best procedure then is to rewrap the AVI as a MOV. There is a good free app called MPEG Streamclip which can do this for you (www.squared5.com).
i have the same problem!
i cannot import any .avi files to premiere cs4. im getting the message "codec missing".
and i tried to transport the files to .mov as you suggested, but the squared5 software is just showing me a blank white screen and no sound, when i open an avi-file.
Get a Windows machine and join the rest of the world.