Apple has posted a knowledge base article about an incompatibility between Xsan 2.1.1 and OS X 10.6:
Do not upgrade computers running Xsan 2.1.1 to Mac OS X v10.6 or Mac OS X Server v10.6 Snow Leopard.
You must install the Xsan 2.2 Update for compatibility with Snow Leopard; this update will be available soon.