Symptom
After updating to Mac OS 9.1, some types of USB modems do not respond properly when attempting to connect to an ISP. With Mac OS 9.0.4 installed, the modem can connect to the Internet service provider (ISP) without any difficulty.
Solution
The standard USB modem driver included in Mac OS 9.1 is based on the USB Communications Device Class (CDC) specifications. Early USB modems that are not compliant with the CDC specifications may no longer behave as expected.
If you have difficulties with your USB modem after updating to Mac OS 9.1, contact the modem manufacturer to ask about an update.
Note: You may be able to restore functionality to your third-party USB modem by reinstalling Mac OS 9.0.4. For information on how to perform a clean installation of Mac OS 9.0.4, see article 60496: "
Mac OS 9: Performing a Clean Installation."