A first time login (initialization) or synchronization fails showing error message "Dynamics NAV:The request failed with HTTP status 401: Unauthorized."
The NAV user in your Anveo User is not allowed to log-in into Microsoft Dynamics NAV.
Re-set Microsoft Dynamics NAV user name and/or password of your Anveo User in Microsoft Dynamics NAV. Re-synchronize Anveo Users to Anveo Server.
Note: This article is for Anveo Client Suite 6 and newer.