Unable to configure the {0} site with the web adaptor. Please make sure that the machine hosting the site is running and that the account specified has administrative privileges

Error Message

Attempts to configure ArcGIS Web Adaptor (IIS) with ArcGIS Server in an ArcGIS Enterprise deployment fail, and return the following error message:

Error:   
Unable to configure the {0} site with the web adaptor. Please make sure that the machine hosting the site is running and that the account specified has administrative privileges.

Cause

The ArcGIS Enterprise deployment is in read-only mode.

Solution or Workaround

Place ArcGIS Enterprise out of read-only mode before configuring ArcGIS Web Adaptor (IIS) with ArcGIS Server. Refer to Portal for ArcGIS: Place ArcGIS Enterprise in read-only mode for instructions.