Mac OS 9.1 includes Open Transport 2.7.4. A significant change in Open Transport 2.7.4 is that Open Transport no longer allows itself to be called at interrupt time. Previous versions of Open Transport did not actively block such calls. This resulted in difficult-to-reproduce software issues that might be perceived as "random" software failures. Because of this, Open Transport 2.7.4 now returns an error if called during interrupt time.
Apple has notified software developers of this change so that applications may be updated. Apple has updated USB Printer Sharing in part for this reason.
If you use a network or Internet-based application that produces a new error under Mac OS 9.1, check for updates to the affected application.
The following article can help you search for a particular vendor's address and phone number:
Article 17159: "
Locating Vendor Information"