Sony Vegas 10, avi importing problem

I'm sure this haas been asked in many different ways, but I can't find one that really helps me.

Sony Vegas Pro won't open .avi files. When I drag and drop onto the timeline I recieve the error message:

"An error occured while opening a codec."

I've been trying so many different codes, it's sent me dizzy!

I know there's the possibility of converting. But it takes quite a lot of space and can take long time, too.

So, could anyone help with this problem, please?

Post a comment in response:

This account has disabled anonymous posting.
If you don't have an account you can create one now.
HTML doesn't work in the subject.
More info about formatting