HI Cedric,
Prognosis 11.1 should be using TLS 2.0 so that older problem with TLS 1.0 being disabled should not be the cause on this one.
On the publish to web window, have you tried different Server and logon names?
Server Name: Maybe try that VIP address you mentioned in the other forum post
Logon: Ensure you are using domain\user naming format
If the above does not help, Can you email me a screenshot of the logon window and the subsequenet error?