Spriting issues - TypeError on line [

Using Web Workbench v 3.2.654.22195 we are experiencing the following error when attempting to generate sprites:

TypeError on line ["27"] of C: can't convert Array into String
Run with --trace to see the full backtrace

At the top of our top-level scss file we have the following:

@import "compass";
@import "img/*.png";
...

and in our config.rb:

# Set this to the root of your project when deployed:
http_path = "/"
css_dir = "public/css"
sass_dir = "sass"
images_dir = "public/css"
javascripts_dir = "javascripts"

where "public/css/img/" is relative to the root of our MVC project

I found that somebody had similar issues with compass some months ago on google groups, but seemingly with no resolution: https://groups.google.com/forum/?fromgroups=#!topic/compass-users/ZChxlt3gRsw

Also, perhaps on a related note, I followed the instructions here on a brand new asp.net web project to see if I could get it working, but there was no "Generate Spriting Import" option available at Step 4: http://www.mindscapehq.com/blog/index.php/2012/10/04/working-with-compass-web-workbench-to-create-button-sprites-within-visual-studio/

Any ideas?

UPDATE - I discovered the cause of the issue. The path names in the config.rb are case-sensitive. On our filesystem, "public/css" is actually "Public/CSS". When I changed the config.rb to reflect this, spriting worked fine.

Case Sensitive Paths

First thing to check is the casing of the paths, it doesn't matter in Windows and to the .NET app, but the ruby compass gem will care.

Ensure your config.rb and SASS files match the exact casing of the directory structure.