I am trying to implement Dashboard widget class (found here: http://harpanet.com/programming/php/codeigniter/dashboard/index#installation) but it is giving me error Unable
Sorry to hear you were having problems, (I've only just noticed this SO entry). Thanks to ReNiSh for his workaround, much appreciated.
You do not however need to use the library approach to implement the 'require_once' of hDash. I have now written a walkthrough for getting hDash installed and running, which you can find here: http://harpanet.com/programming/php/codeigniter/dashboard/walkthrough
Also, note that as of yesterday, 3rd Feb 2014, hDash has been updated to version 1.2.