From memory
1. Can you connect to the windows 2012 vm remotely? The vm might use an internal network.
2. SQL Configuration Manager: is TCP protocol enabled?
3. The SQL Server instance is set for fixed network ports (dynamic ports may mess up the firewall)
4. SPN's are set ? (especially when authenticating with windows/Kerberos).
5. Double check firewalls at both sides (client & server)
6. SSRS has its own access-configuration (at start it is restricted to buildin administrators)
There must be a connectivity guide for SSRS on the web somewhere