Well the biggest "proof" I have is that I rebooted my network this weekend and for a couple of days I Limited the size to just my media network + 2 PCs, and everything seemed to work fine, a couple of days later the when I had added all the other Devices to the network I started getting the same issue again, after showing my logs to the MediaPortal People who understand it I recieved the following answer.
The problem is with the communication between the client and server.
Failed to get a SDP description from URL rtsp://TV-Server:554/stream3.0 connect() failed: Unknown error
Check your networking and perhaps try using static IP addresses instead of hostnames.
Ok, quick primer as we do not know your experience level.
If we think of the system as a personal phone book.
The DNS server is the person holding the phone book, the host name is the persons name and the IP address is their telephone number. If you want to call someone then you can either use their telephone number directly (IP address) or you can ask the person holding the phone book (DNS server) for the number relating to the person you want to contact (Hostname).
In the case of most standard home setups, the phonebook holder is a person (machine) on their Internet service providers network and this holder needs to record lots of different sets of details for all the different people using the service and sometimes gets a bit confused. It then may have problems giving the correct address for a set machine.
Adding to this that a lot of setups also have DHCP which is like having the ability to change phone numbers (using the above analogy) on a regular basis and you have a greater chance of the phonebook holder missing entries / getting confused.
Some people fix this by having their own phonebook holder on their own network (personal DNS server) but this can cause different issues especially if not configured correctly.
Another possibility is that one of your machines is set to use a static IP address and is using the one assigned to your server or vice versa. If there are two machines on your network both using the same address then much confusion can ensue.
To check for this, go back to the last known config that worked (server and a few machines), verify it is working and then add a device to your network one at a time and verify after each addition. If an IP address clash is occurring then this should help you to find out which machine is clashing with your server and then you can try to narrow down why.
I would take the time to resolve the issue rather than trying to find a way around it as you could just hit the same problem again whatever solution is suggested.
Let us know how you get on.
RB
On most home networks I have dealt with, the DNS servers are the ISPs and, as Cactus has said, don't always work well when capturing the hostnames of your machines on your lan so the actual addresses (IP addresses) can be referenced for the communication to the physical computer.
