Fix: SharePoint 2010 – Web application at URL could not be found on calling SPSite.OpenWeb/SPSite.AllWebs exception

I wanted to access SharePoint document library from a WCF service but it was throwing the exception on SPSite.OpenWeb/SPSite.AllWebs method calls as displayed below“The Web application at could not be found. Verify that you have typed the URL correctly. If the URL should be serving existing content