Symptoms

When trying to access the workflow designer using K2 Appit for SharePoint you are prompted to install Silverlight. Even when you have previously enabled NPAPI flags within Google Chrome.

As specified in the article: http://help.k2.com/kb001699
 

Diagnoses

As of the Google Chrome 4.5 update, the NPAPI plugin is no longer supported by Chrome. As such, the option to enable this functionality is no longer present within the browser.
 

Resolution

The only solution is to use an alternative browser such as Internet explorer (versions 9 and up) and Firefox. These browsers continue to support Silverlight functionality.