Following up to my own post, I've discovered some information in the log files:
17:26:37,147 ERROR [org.alfresco.web.ui.common.Utils] A system error happened during the operation: Could not execute JDBC batch update
org.hibernate.exception.GenericJDBCException: Could not execute JDBC batch update
at org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:103)
at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:91)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:249)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:235)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:139)
at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:298)
at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:27)
at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1000)
at org.alfresco.repo.avm.hibernate.AVMNodeDAOHibernate.flush(AVMNodeDAOHibernate.java:175)
at org.alfresco.repo.avm.AVMStoreImpl.createFile(AVMStoreImpl.java:488)
at org.alfresco.repo.avm.AVMRepository.createFile(AVMRepository.java:269)
at org.alfresco.repo.avm.AVMServiceImpl.createFile(AVMServiceImpl.java:394)
at org.alfresco.repo.avm.AVMLockingAwareService.createFile(AVMLockingAwareService.java:904)
at sun.reflect.GeneratedMethodAccessor1253.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:281)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:187)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:154)
at org.alfresco.repo.search.AVMSnapShotTriggeredIndexingMethodInterceptor.invoke(AVMSnapShotTriggeredIndexingMethodInterceptor.j
ava:154) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:176)
at org.alfresco.repo.transaction.RetryingTransactionAdvice.invoke(RetryingTransactionAdvice.java:92)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:176)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:210)
at $Proxy22.createFile(Unknown Source)
at org.alfresco.web.bean.wcm.ImportWebsiteDialog.importDirectory(ImportWebsiteDialog.java:347)
at org.alfresco.web.bean.wcm.ImportWebsiteDialog.importDirectory(ImportWebsiteDialog.java:389)
at org.alfresco.web.bean.wcm.ImportWebsiteDialog.importDirectory(ImportWebsiteDialog.java:389)
at org.alfresco.web.bean.wcm.ImportWebsiteDialog.importDirectory(ImportWebsiteDialog.java:389)
at org.alfresco.web.bean.wcm.ImportWebsiteDialog.processZipImport(ImportWebsiteDialog.java:309)
at org.alfresco.web.bean.wcm.ImportWebsiteDialog.finish(ImportWebsiteDialog.java:210)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.apache.myfaces.el.MethodBindingImpl.invoke(MethodBindingImpl.java:132)
at org.apache.myfaces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:61)
at javax.faces.component.UICommand.broadcast(UICommand.java:109)
at javax.faces.component.UIViewRoot._broadcastForPhase(UIViewRoot.java:97)
at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:171)
at org.apache.myfaces.lifecycle.InvokeApplicationExecutor.execute(InvokeApplicationExecutor.java:32)
at org.apache.myfaces.lifecycle.LifecycleImpl.executePhase(LifecycleImpl.java:95)
at org.apache.myfaces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:70)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:139)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
at org.alfresco.web.app.servlet.AuthenticationFilter.doFilter(AuthenticationFilter.java:81)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:215)