I've had this issue lately on other developers SASS projects where the Google CDN import won't compile -- See screenshots, saves fine when commented out.
I read a few articles on this issue and it was suggested to do this command:
gem install compass
I don't use compass, I use a SASS plugin for Coda. Guessing the previous developer used Compass to compile? Figured this might help the compiling issue.
The Sass import code should look like this:
@import url(http://fonts.googleapis.com/css?family=Open+Sans:300italic,400italic,700italic,400,300,700);
You are importing from an URL, but your code is written as if you were importing a local file—that is why the error message says it can't be found.
Here's a little tutorial on how to use Google fonts with Sass.