Networking firms who have found that their software no longer works with Macs running Mac OS X Tiger are blaming Apple for re-writing the kernel in Mac OS X.

Cisco was the first to announce that its VPN software was incompatible with Tiger, now Thursby Software has admitted that it needs to redesign its kernel extensions to work with Tiger. "A major job for us," according to Thursby CTO Paul Nelson.

Nelson explained that, with Tiger, Apple has created a new set of kernel programming interfaces that change the way the operating system works with software written directly to its kernel. "The move rendered obsolete some longstanding Unix networking program methods, known as Berkeley protocol stack," writes Cnet.

Microsoft is also reporting problems with the Virtual Switch networking feature of its Virtual PC software. Microsoft's zero-configuration printing and ability to launch PC programs via the dock is also affected.

Lobotomo Software and Equinux have also issued incompatibility warnings.

Thursby hopes to have updated versions of its ADmitMac and DAVE products by August. Microsoft is "working closely with Apple" and hopes to have a patch within "two to three months".