Is there any specific things I should be aware of when moving from mySQL to MSSQL 2005?

Running under JBoss, and the only thing I've changed is the -ds.xml connection file, and the sqldialect setting in persistence.xml.

Most things work as before, but a many- to-many mapping bombs out with a:
12:42:36,856 ERROR [LazyInitializationException] could not initialize proxy - no Session
org.hibernate.LazyInitializationException: could not initialize proxy - no Session
at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:57)
at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:111)
at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:166)
at com.markedskraft.analyseweb.ejb3.user.Organisation_$$_javassist_3.getPackages(Organisation_$$_javassist_3.java)
at com.markedskraft.analyseweb.web.MainServlet.hasAccess(MainServlet.java:268)
...

TIA...

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Dag.