Symptoms

Customer received the following error when click on Viewflow from SharePoint site:
Server Error in ‘/Viewflow’ Application
Runtime Error
 

Diagnoses

Go to k2 workflow history of any documents and there is link "View Flow", click on it, it will throw exception.
E.g. Open Menu dialog "VM Test" document, then click on K2 workflow, then View Flow
https://share.*****.net/sites/infopoint-dev/New Document Library/Forms/AllItems.aspx
 

Resolution

We are able to see flow when selecting Azure as authentication method.
They also had to change the target framework in app pool to 4 as it was referring 4.5.