This error i got when I'm opening a SharePoint Task from MS Outlook. So it is pretty forward. You need to add the source site to the Trusted Sites in the IE (Internet Explorer) or ask network security admin to trust it from the proxy policies.
Monday, November 28, 2011
Friday, November 4, 2011
Security settings for this service require Windows Authentication but it is not enabled for the IIS application that hosts this service.
There can be many reasons for this. but before checking any of those web configuration things check the Authentication section in the virtual directory in IIS.