"A person answered instead of a modem."

This error you will probably never see, if you call someone with your modem accidentally, windows won't report it as this error..

We're all put in a wrong number or type in the dial string for our modems at least once in our lives. Most common error here is that we simply made a typo or didn't add the 9 in front of the phone number if needed. Doublecheck the phone number.

Also in some cases its an old number that your ISP has given back to the telco and has been reassigned (not as common in ISP days as it was in old BBS days..)

I'd suggest turning up the modem speaker on your computer (in windows) and see if you hear a person, or do you get the bell recording saying "I'm sorry, this number is unassigned"..

But generally doublecheck the number you are calling is typed in correctly