Based on vendor alerts as well as reports from forums and blogs in Gearwire's space, something appears to be amiss with Apple's most recent OSX software upgrade, 10.4.9. Plugin maker Ohm Force sent the following to Gearwire (in French naturellement, translation courtesy of Babelfish:)

Important Note Caution: the installation of 10.4.9 can empcher the operation of our plug-ins AudioUnits. 10.4.9 installs a new version of auval, with which our plug-ins WITH is incompatible. We did not think that this version would be publi?e before the exit of 10.5 We wish to put a new version? day which will pass the validation within 3 weeks. Meanwhile, we advise you not to install 10.4.9. D?sol? for d?rangement, Ohm TEAM

While it could be made clearer, it seems that Ohm Force is advising users to not apply the 10.4.9 upgrade specifically due to changes in the AU subsystem.

Gearwire has not yet applied the upgrade.

Other evidence of weird and unexpected changes comes from warnings issued by Waves, Synful (complaints about iLok problems ) and even some mumblings about TC Powercore plugs being lost at DAW load time.

A quick summary of reportedly affected products/systems:

• Waves
• QuickTime
• AU in general via AUval API element
• iLok
• Ohm Force
• TC Powercore

Watch Gearwire for more news from Apple and affected customers on this OS upgrade problem.