If you have configured DUN to redial your ISP, you may receive the following after 15 attempts:

Could not detect modem. It may be in use, turned off, or not installed properly.

If your modem is based upon the Rockwell chip set or USR/3Com set, it may have blacklisting enabled. The ITU standard dictates that the modem blacklist the phone number after 15 failed attemps.

If this happens, you must wait for the modems internal time-out or you must reboot.

You can turn off blacklisting by modifing the modem initialization string:

    Command  Modem type                                  %TCB     Rockwell based                                  S40=2    U.S. Robotics/3Com                                  S40=7    U.S. Robotics/3Com
You may want to contact your manufacturer for an updated .inf file.