KB ID 0001659 Problem While trying to fix another Azure AD Replication problem today I managed to delete one of the connectors (the one for the local ‘on-prem’ Active Directory). In an effort to ‘recreate’ it, I ran the ‘Microsoft Azure Active Directory Connect’ and went to ‘Customise the Synchronisation Options’.  Unfortunately I got this error; The forest {forest-name} cannot be added because the attribute used to uniquely identify your users in Azure AD (mS-DS-ConsistencyGuid) is already in use. Thats not good! I was starting to get concerned....