(unspecified) error when compiling a CSS-file 

I tried to minify a CSS file.
The file was first compiled from a sass-file to "compressed"-format.
Then i used the settings: 
- automatic compiling
- combine import
- "yuicompress"

I get this error message:

```
---error---
/Applications/Koala.app/Contents/Resources/app.nw/app/scripts/compilers/CssCompiler.js:83
Uncaught TypeError: Cannot read property '1' of null
```

Hope this helps :-)
