I got a call last week from a friend that brought back memories of the bad old days of networking computers. He'd been issued a new notebook at work, preconfigured with all of the business applications and antivirus and security software that his company required, and he wanted to be able to use it on his home network, as his company's use policy permitted. He'd run into a bit of a snag, however, and his skills as a knowledgeable computer user weren't up to the task.

My friend could connect to the Internet from home, run his VPN software, and connect to his corporate network resources without a problem. However, he wasn't able to access files on his notebook from any other computer on the home network.

A little phone diagnosis made clear that the basic network connections weren't the problem--after I walked him through some basic networking diagnostics, we determined that although his new notebook could see the network, the rest of the home network couldn't see his notebook. He'd already run the Network Setup Wizard and the Wireless Network Setup Wizard in an attempt to solve his problem, but to no avail.

My next question was the obvious: Are you running a firewall on the individual clients or using a hardware firewall in your Internet router? He was using both: the hardware firewall that came with his router, and Windows Firewall, which had defaulted to "on" with his installation of Windows XP Service Pack 2 (SP2). However, he'd already disabled Windows Firewall on all the computers for the purpose of determining whether it was a problem, so he was fairly certain that it wasn't.

While I walked him through the diagnostic procedure, he was searching the Web and coming up with all sorts of potential Windows issues that could have been causing his problem. As a result, he developed a severe case of computer hypochondria. He was sure that he was the victim of all sorts of Windows security problems and that his only recourse was to give up, since he couldn't follow some of the recommendations he was finding on the Web that required making major changes to the computer OS, which he couldn't do on a work computer.

At that point, I asked him what processes were running on the computer. As he iterated them, I discovered that one of them was Zone Labs' ZoneAlarm firewall. Apparently his employer's IT technicians installed ZoneAlarm but didn't disable Windows Firewall. Although I'm not sure how it happened, as soon as we reconfigured ZoneAlarm to allow traffic on the local network, all of his connectivity problems disappeared.

In and of itself, my friend's problem wasn't a big deal--dealing with network configuration problems and a computer's inability to see network resources used to be fairly commonplace. But if you're an IT pro who supports hundreds of remote users, a simple configuration error like that one can result in hundreds of hours of lost productivity. Remember that every configuration change made to a computer will have an impact on its use. If you're allowing home use of company computers or configuring computers for telecommuters, you should consider all the potential uses of those computers.