Why cant I import a .avi file?

When you look at the item properties in Explorer, what video compression (CODEC) is indicated?

Are you able to play the file in VLC Player?

avive33  wrote i downloaded and installed k lite

Unfortunately, you followed terrible advice.  K-Lite has been known to overwrite codecs installed by the system and Adobe and may require a reinstallation of the operating system and Adobe programs to repair that issue.

So first - even if it is a 600fps you can convert it but you need to use codec that support that kind of fps. Second - does not matter if you instal k-lite or any other codec pack. you have to know what codec was used to compress your AVI file, then check if AE is supporting it, and if it supports that codec - try to install that exact codec.
Or if AE does not support that codec at all - you have - as i said - to convert it. But first thing that you have to know is what codec was used for compression of your original file. Or if you are not able to do that - maby you know from what device is that file.