Many users have run into ClassNotFoundExceptions and NoClassDefFoundErrors after working with web services that target GlassFish while developing their projects in NetBeans. The issue usually appears as a dialog similar to this This can be pretty debilitating. The bug appears to be in the AntClassLoader, which is tickled by the wsimport ant task that ships with GlassFish 3.1.2. The fix is pretty simple: Upgrade the Metro bits that ship in 3.1.2 with bits that have had a patch applied. There are detailed instruction about installing the updated Metro bits onto GlassFish. This upgrade is probably useful for any install of GlassFish 3.1, but it is critically important for folks that develop web services from inside NetBeans and deploy them onto GlassFish 3.1.2.