I had a momentary few minutes where I could not connect to the SB2008 Server through Teamviewer Client nor RDP through VPN, I was able to ping the SBServer from another Server successfully and I could rdp to the other application servers, I was also told the Exchange 2007 was not functioning at that time as well. After a few minutes I was able to access the SBSServer2008 and everything was functioning as normal. I reviewed the Event logs and under System the only abnormality was: RasSstp Error (Event24) and Warning (Event 18).
I am not sure these Events are the culprit but wanted to pose this question out to see if anyone has had any similar situation with an interruption like this. No DNS Issue found as well.
1) Network reconfiguration: If the NIC was in the process of reconfiguring, you could get denied access like this. A common reason for this is a faulty cable that is not true Cat5E(or higher) and attempting to use GbE connection. I've seen the NIC reconfigure itself for 100Mbps, then switch back to GbE -- all on its own.
2) Busy NIC: If a process was consuming all of the network bandwidth for a period of time (such as backup, large file copy, etc.), then connection-based processes can have problems connecting in a timely manner. PING, which is a simple UDP packet, may be able to squeeze through.
3) Switching or networking problem: The problem may not be specific to the server, but rather to a switch to which it is connected. If someone created a switching loop, routing loop, or the like, then communications can fail.
4) Another machine came up with that IP address: This is the more scary option -- another PC could be trying to use the same IP address as the server. The PING works, but you were actually pinging the wrong system. If it happens again, check the ARP table after the PING to verify that the correct machine responded. This could also be indicative of an attempted Man-In-The-Middle attack, where network packets are being re-routed to a bad host.
5) Major CPU issue: if the server CPU was very busy and unable to process the connection requests in a timely manner, then this symptom could be seen. Again, PING replies are very easy and require little to no CPU time. Setting up a new RDP session, OTOH, takes some real work.
To tell for sure, you can use Wireshark or some other network analysis tool connected to the same core switch, monitoring traffic from that server, and see what is responding (and what isn't) when the problem occurs.