Unable to access RDP session of a host in a Windows 2012 RDS farm.

We have a Windows 2012 RDS farm that contains 3 RDS hosts.  When I try to access a published app as a domain user, I am getting an error "The user was denied access".  

When I try to RDP to a farm host as a domain user, I am getting "The requested session access is denied".  

I have already made sure the local Remote Desktop User Group includes mydomain\domain users. 

Please advise where I should look at.  

Thanks,