Unable to configure the ArcGIS Server site with the web adaptor (IIS) (11.3)

[PieterHoltzhausen1]

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 ?

[valenj88]

In a web browser, go to: https://sita-qa-law01.drdlr.gov.za:6443/arcgis/admin/upgrade
Upgrade the server
Then try and bind the web adapter.

[PieterHoltzhausen1]

I was able to get it to work, but with the following configuration:
ArcGIS Server 11.3
ArcGIS Web Adaptor (IIS) 10.9.1

order of steps are important:
do not uninstall ArcGIS web adaptor 10.9.1
upgrade ArcGIS server 11.3
complete upgrade via https://sita-qa-law01.drdlr.gov.za:6443/arcgis/admin/upgrade

[vipulsoni]

The ArcGIS 11.3 will work with the latest web adaptor, try once entering the same old password in the WebAdaptor 11.3 to add the GIS Server (its sounds crazy but somehow the old user password combination is saved somewhere which the new web adaptor needs). 

[MaartendeJong]

It might help to set the password for the primary site administrator again in 

https://<DNS>/arcgis/admin/security/psa/update