Then the most possible reason for the error is that
1. The linked server database is stopped. 2. The linked server database is occupied with other stuff (reindexing, backup). 3. The linked server is down (power off). 4. The linked server is busy with other stuff (defragmenting). 5. A cable to the linked server is dropped (replug all cables). 6. A router/switch/hub is faulty or not working. 7. Too much data is passed on the network.