find the account that runs the Qlik Sense services. Go to QMC and add the "Root Admin" role to it. This will ensure the account has access to the "qrs_*" data connections. Make the sa_ accounts "Root Admin" as well.
My account had all admin rights and still did not work. We realized that the system admins had not added the Qlik group to the service account created in AD. So, if you are using Active Directory, don't forget to add the Qlik group to the service account. Other wise, the service account in Qlik will be Inactive and Removed Externally in QMC.