Some new facts: 1)Trying the BETA release of JBossCache results in the same error. 2) If I try to persist an object with just strings and ints (i.e. no collections) then this configuration works. However, trying to persist an object with a collection is what is causing the error. The hbm file of the object I'm trying to persist is: | <hibernate-mapping package="com.qxlva.mm.dispensing.loadtest.model"> | | <class name="ManagerDetails" table="MANAGER_DETAILS" dynamic-update="true" dynamic-insert="true"> | <id name="iid" column="MANAGER_DETAILS_IID" type="long"> | <generator class="seqhilo"> | <param name="sequence">MANAGER_DETAILS_SEQUENCE</param> | <param name="max_lo">10</param> | </generator> | </ | <property name="monitorChannelDetails" type="string" length="1000"/> | <property name="testReady" type="boolean"/> | <property name="testInitialised" type="boolean"/> | <property name="testRunning" type=" | <set name="certificates" cascade="all-delete-orphan" lazy="false" outer-join="false"> | <key column="MANAGER_DETAILS_IID"/> | <one-to-many class="com.qxlva.mm.dispensing.loadtest.model.CertificateCredentials"/> | </ | </class> | | </hibernate-mapping> and the object that hangs off it contains no collections: <hibernate-mapping package="com.qxlva.mm.dispensing.loadtest.model"> | <class name="CertificateCredentials" table="CERTIFICATE_CREDENTIALS" lazy="false"> | <id name="iid" type="long" column="CERTIFICATE_CREDENTIALS_IID"> | <generator class="seqhilo"> | <param name="sequence">CERT_CRED_SEQUENCE</param> | <param name="max_lo">5000</param> | </generator> | </id> | <property name="filename" type="string" column="FILENAME"/> | <property name="keystoreType" type="string" column="KEYSTORE_TYPE"/> | <property name="password" type="string" column="PASSWORD"/> | <property name="username" type="string" column="USERNAME"/> | <property name="inUse" type="boolean" column="IN_USE"/> | <property name="ssoToken" type="string" column="SSO_TOKEN"/> | <property name="ssoTokenExpiryTime" type="org.joda.time.contrib.hibernate.PersistentDateTime" | column="SSO_TOKEN_EXPIRY_TIME"/> | </class> | | </hibernate-mapping> As I say, I can successfully persist a CertificateCredential with thie treecache.xml and hibernate.cfg.xml files supplied. However as soon as I try to persist a ManagerDetails which has a collection of CertificateCredentials, the NPE is thrown. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4040206#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...