The Mac OS X 10.2.4 update is causing problems for a number of users and third-party developers.
In 10.2.4, Apple changed the PPP (Peer-to-peer protocol) stack, a feature required by peripheral devices such as modems.
Hermstedt's WebShutte ADSL modem has been affected, and users will find their modem stops working once OS X 10.2.4 is installed.
Hermstedt's UK managing director Andy Eakins said: "We had very little notice of the update, and were not informed when it would be released."
Hermstedt is working on a software fix for the problem. The company's engineers are understood to have been dealing with it over the weekend. Hermstedt expects to release the software update tomorrow morning. It will be available for download from the company's Web site. Hermstedt will also mail out CDs containing the update upon request.
Other issues caused by the update include synchronization and pairing problems using Bluetooth devices and iBook modem problems.
Eakins said: "Why is there no uninstaller option for OS X updates? Apple does not warn that its updates can cause problems, and its users install them as soon as they are released. It causes major problems to Apple's developers."
He added: "It's another argument for distributing such updates on cover CDs, so that Apple's users can beta test the software and Apple can fix the problems."
Macworld is hosting a forum in which readers can report problems encountered with the update and share solutions.