The Help File column in the July 10 Business section incorrectly described Cox Communications' digital telephone service. Cox transmits phone calls over the same cable lines used for TV programming but reserves a fixed amount of its cable bandwidth for them. (Published 07/16/05).

QWe are considering switching from our Cox digital phone service to Vonage. What are the advantages and disadvantages of each?

AVonage and other voice over Internet protocol services -- in which calls travel as digital bits over a broadband Internet connection -- should cost a lot less, especially for long-distance and international calling. Most VoIP packages also bundle many more calling features, including slick voice-mail and call-forwarding options.

But with VoIP, you run the risk of getting less reliable phone service. If your Internet connection drops, you have no phone service at all, and voice quality can degrade in heavy Internet traffic.

Cox Communications' phone service, by contrast, is built like other land-line phone systems: This cable company runs a separate wire to your house to carry phone traffic. Therefore, it should be just as reliable as any local phone service. But Cox's basic plan also costs only a dollar or two less than Verizon's equivalent, with larger savings if you start piling on calling features.

When I turn on my computer, I get a message that "mm_tray.exe" couldn't start because "CoreDll.dll was not found." Any ideas?

That "mm_tray" file is a component of the MusicMatch jukebox program. It puts a shortcut to that program in the system tray, the bottom-right segment of the Windows task bar that seems to fill up with meaningless icons.

Reinstalling or uninstalling MusicMatch should fix the issue.

This is yet another example of why I don't like applications that treat the tray like a billboard. Not only do the overwhelming majority of these tray components fail to do anything useful, they're also yet another moving part that can break. Windows XP can hide these nuisances, but what it desperately needs is a way to blast them off your hard drive.

-- Rob Pegoraro

Rob Pegoraro attempts to untangle computing conundrums and errant electronics each week. Send questions to The Washington Post, 1150 15th St. NW, Washington, D.C. 20071 or