We have a domain-joined RDS 2008 R2 server where logons are rejected for domain accounts (even domain admins) coming in directly over the internet, but it works fine over VPN or internally.

The RDS server also has a number of local accounts, and those logons work fine directly over the internet or over VPN. The domain is controlled by SBS 2003.

Some configuration and locking down was done long ago on this server, so I'm not sure if this is due to some configuration or it's a Windows issue.

I don't think it is a Windows or hardware firewall issue, since the attempted RDP logon reaches the server. The failed logon is recorded in the Event Viewer:

```
        An account failed to log on.
        Subject:
            Security ID:        NULL SID
            Account Name:       -
            Account Domain:     -
            Logon ID:       0x0

        Logon Type:         3
        Account For Which Logon Failed:
            Security ID:        NULL SID
            Account Name:       testuser
            Account Domain:     testdomain
        Failure Information:
            Failure Reason:     An Error occured during Logon.
            Status:         0xc000006d
            Sub Status:     0x0
        Process Information:
            Caller Process ID:  0x0
            Caller Process Name:    -
        Network Information:
            Workstation Name:   testPC
            Source Network Address: -
            Source Port:        -
        Detailed Authentication Information:
            Logon Process:      NtLmSsp 
            Authentication Package: NTLM
            Transited Services: -
            Package Name (NTLM only):   -
            Key Length:     0

```

All the single dashes above are verbatim from the log entry, I did not insert them for privacy.