You will need to delete this page by going into the web parts maintenance page (?contents=1 ) and closing or deleting the webpart and then will need to change the credentials defined for the namespace

Refer the following Link : http://www.c-sharpcorner.com/UploadFile/22da8c/sharepoint-server-2013-a-duplicate-field-name-xxx-was-fou/ https://support.microsoft.com/en-us/help/3019110/fix-duplicate-names-are-not-allowed-error-when-you-add-multiple-filter