Question : Have to clear arp cache to get on internet

We have a network of about 50 users and 5 servers. We also have a sonicwall firewall connected to a cisco 1700 which connects to our T1. We have two switches, one HP and one Netgear.
We had a power outage that lasted about 4 hours. We were able to shut everything down gracefully. When everything came back up, we noticed intermittent issues with connectivity. We noticed that one of our terminal servers was not responding to outside connections and our website could not be accessed from the outside. At times when the servers are not responding to the outside, they cannot bring up a web page or even ping our default gateway. I have found that if I clear the arp cache on the box having the issue, everything is fine.
 This also happens on some workstations. After a period of inactivity, the workstations will not be able to get to the internet. When this happens, I cannot ping the gateway (sonicwall firewall). If i clear the arp cache, everything works. For now I have created static arp entries in the firewall for the webserver and terminal server and they have been working fine. Obviously I can' do this for all workstations.
I called sonicwall and they were no help.

Answer : Have to clear arp cache to get on internet

re-create the problem, then run a network sniffer (i.e. Wireshark) on the internal client, while you ping the gateway. Without a sniffer you can only guess what's happening on the network. If the client sends the ICMP ECHO packet to the correct MAC address, and the firewall does not answer, it's clearly a problem with the firewall. You should then go back to SonicWall support and show them your capture file and ask for an explanation ;-)