Then I immediately sign on again and the connection will be fine for as long as I stay on. When the connection is lost AOL reports a carrier lost message received from the modem. I use AOL 4.0 and an external US Robotics 56K v.90 modem on my 200 Mhz Acer Aspire. The Aspire comes with a 33.6 bps internal modem and it never would lose the AOL connection. I still have that modem connected on COM2 and the 56K is on COM1.
Chances are the modem setting is wrong on the first setting and correct on the fallback.
In other words, the AOL software is treating your new modem as though it had the settings of your old one. So, you need to click on the Setup button on the America Online sign-on screen and then chose Expert Add. That will take you to a box where you can set both the modem and the phone number for first try and for fallback.