Access is Denied company "xxxxx"

I have recently successfully upgrade from NAV2009R2 to 2017 and tested on my LAPTOP, But on installation at the client I am having issues trying accessing the company in RTC i am getting an access denied error to the company. So because of training deadlines I configured NAV for web client and created a user with NavUserPassword Authentication and did not get any problem with this user (implying that users configured for NavUserAuthentication are Okay whether RTC or Web Client) but later will have to use the RTC since there is a alot more work to do. Could you be having an Idea where this is coming from?

NB: I am installing on a VM running server 12R2 and SQL 2016.