Library - class file was not found - How to track error

[eluser]sanguina[/eluser]
How do i go about tracking the message - "class file was not found"

For this particular case,

I am using PhPass library - pasted that in the libraries folder.
then I am calling it like this:

Code:

$this->load->library('phpass');
$password = $this->phpass->hash($password);

the library is definitely getting loaded (or else i would have a library not found error)

rather i am getting the error:

"class phpass not found."

I can clearly see the class defined in the aforesaid library but i still get this message.

Any suggestions, thanks