Symptoms

When loading the K2 for SharePoint 2013 Worklist Webpart onto a SharePoint 2013 native mode page, an error is displayed saying that the content of the control cannot be displayed in a frame. This usually happens in SharePoint Online installations of the app.
 

Diagnoses

This is a known issue having to do with which trusted sites live in the IE browser for the user(s) trying to access the Worklist Webpart.
 

Resolution

The following steps can be taken to resolve the issue with a SharePoint Online installation:

1) Add “https://login.microsoftonline.com” to the Trusted Sites list in Internet Explorer. Also check that the list of sites below is already in the Trusted Sites list, otherwise add those sites to the Trusted Sites list as well:
• https://.sharepoint.com
• https://-my.sharepoint.com"
• https://-admin.sharepoint.com
(where is the name of the user’s SharePoint online site. Making this configuration changes will prevent this error from occurring for that user)

2) Clear the IE cache (Tools, Internet Options, on the General tab click “Delete” under Browser history, make sure to check at least “Temporary Internet files and website files” and “cookies and website data”, delete)

3) Close and reopen IE.