org.datanucleus.store.rdbms.sql.expression.DelegatedExpression#delegate is inaccessible by subclasses in plugins if running in an OSGi environment: the field is package private and thus can only be accessed by classes in the same package AND which are loaded by the same classloader. In OSGi, plugins are bundles which use their own classloaders.
Subclasses in plugins (e.g. org.datanucleus.store.rdbms.sql.expression.JodaDateTimeLiteral) try to access this field, which results in an IllegalAccessError.
My suggestion would be to make the field protected, since it only appears to be accessed by subclasses.