I have upgraded from ArcGIS Server 10.9.1 to 11.3 on our QA server.
After the upgrade I installed the IIS web adaptor for 11.3, with it's dependencies.
When I want to configure the web adaptor I get the following error message:
Unable to configure the ArcGIS Server site with the web adaptor. Please make sure that the machine hosting the site is running and that the account specified has administrative privileges.


I tried the following thus far with no success:
Gave full access to ArcGIS account on folders C:\arcgisserver and C:\Program Files\ArcGIS\Server
Reset my password for siteadmin admin account
Added the ip and DNS alias to the etc/hosts file (this worked for 10.9.1 but not for 11.x)
I can access the manager via https://sita-qa-law01.drdlr.gov.za:6443/arcgis/manager
Anything else I could try ?