If you find that VTS reports a modem as permanently unavailable, you may find that the modem event log indicates that a TAPI error is occurring. While a full list of such errors is given in Call Progress and Error Codes, in the vast majority of cases, this will be caused by one of two things:
• The system has not been rebooted since the modems were last reconfigured. While a reboot is not always required, after some reconfiguration actions the system cannot enumerate the resources correctly until a reboot has occurred.
• Some non-TAPI-compliant application has opened the serial port associated with the modem. Note that this includes VTS's ComPort function and the system's HyperTerminal application (commonly used in troubleshooting modems).