Last week TUAW reported that the Thunderbolt 1.2 update, which was released to provide support for the new US$29 Apple Thunderbolt to Gigabit Ethernet adapter, was causing some Macs to experience boot failures that often required a complete reinstall of Lion to resolve. Well, Apple apparently jumped on the problem as soon as it was reported, as a new Thunderbolt 1.2.1 update that fixes the problem is now available.

If you're using a Thunderbolt-equipped Mac with OS X Lion 10.7.4, then the update will appear in Software Update for easy installation. As usual, Apple has made a direct download link available.