Hibernate JDBCConnectionException: could not update

In a Java + Hibernate aplication, we get a JDBCConnectionException:

org.hibernate.exception.JDBCConnectionException: could not update: [net.gencat.cultura.itinerarisLectura.model.AppVariables#14]
    at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:74)
    at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
    at org.hibernate.persister.entity.AbstractEntityPersister.update(AbstractEntityPersister.java:2421)
    at org.hibernate.persister.entity.AbstractEntityPersister.updateOrInsert(AbstractEntityPersister.java:2303)
    at org.hibernate.persister.entity.AbstractEntityPersister.update(AbstractEntityPersister.java:2603)
    at org.hibernate.action.EntityUpdateAction.execute(EntityUpdateAction.java:92)
    at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:248)
    at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:232)
    at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:140)
    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 hibernate.util.ManagedSession.rollbackTransaction(ManagedSession.java:64)
    at net.gencat.cultura.itinerarisLectura.model.home.AppVariablesHome.attachDirty(AppVariablesHome.java:122)
    at net.gencat.cultura.itinerarisLectura.struts.action.AppVariablesAction.save(AppVariablesAction.java:157)
    at sun.reflect.GeneratedMethodAccessor1526.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:280)
    at org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:216)
    at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:484)
    at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)
    at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
    at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
    at net.gencat.cultura.itinerarisLectura.filters.LoginFilter.doFilter(LoginFilter.java:82)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
    at org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:199)
    at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:282)
    at org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:767)
    at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:697)
    at org.apache.jk.common.ChannelSocket$SocketConnection.runIt(ChannelSocket.java:889)
    at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
    at java.lang.Thread.run(Unknown Source)
Caused by: com.microsoft.sqlserver.jdbc.SQLServerException: Se ha producido una excepción durante el método DBComms.receiv开发者_JAVA技巧e. Operación:Connection reset. Contexto:(173) [Thread[TP-Processor14,5,main], IO:a9a8a, Dbc:53c34]. PktNum:0. TotalReceived:0. PktSize:4.096.
    at com.microsoft.sqlserver.jdbc.SQLServerException.makeFromDriverError(Unknown Source)
    at com.microsoft.sqlserver.jdbc.DBComms.receive(Unknown Source)
    at com.microsoft.sqlserver.jdbc.SQLServerPreparedStatement.doExecutePreparedStatement(Unknown Source)
    at com.microsoft.sqlserver.jdbc.SQLServerPreparedStatement$PreparedStatementExecutionRequest.executeStatement(Unknown Source)
    at com.microsoft.sqlserver.jdbc.CancelableRequest.execute(Unknown Source)
    at com.microsoft.sqlserver.jdbc.SQLServerConnection.executeRequest(Unknown Source)
    at com.microsoft.sqlserver.jdbc.SQLServerPreparedStatement.executeUpdate(Unknown Source)
    at com.mchange.v2.c3p0.impl.NewProxyPreparedStatement.executeUpdate(NewProxyPreparedStatement.java:105)
    at org.hibernate.jdbc.NonBatchingBatcher.addToBatch(NonBatchingBatcher.java:23)
    at org.hibernate.persister.entity.AbstractEntityPersister.update(AbstractEntityPersister.java:2399)
    ... 41 more

What could be? Problem of the Database? Programming bug? Hibernate bad configuration? "Luckily" it only fails in the production database, we can't reproduce at local.

The hibernate.cfg.xml

<property name="current_session_context_class">thread</property>

 <!-- Use the C3P0 connection pool. -->
    <property name="c3p0.min_size">3</property>
    <property name="c3p0.max_size">100</property>
    <property name="c3p0.timeout">1800</property>
    <property name="c3p0.max_statements">50</property>

    <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>
    <property name="cache.use_query_cache">false</property>
    <property name="cache.use_minimal_puts">false</property>
    <property name="max_fetch_depth">3</property>

EDIT:

At the same log file I also get the next message, that could be important

WARN  [TP-Processor7] com.mchange.v2.c3p0.impl.NewPooledConnection - [c3p0] A PooledConnection that has already signalled a Connection error is still in use!
WARN  [TP-Processor7] com.mchange.v2.c3p0.impl.NewPooledConnection - [c3p0] Another error has occurred [ com.microsoft.sqlserver.jdbc.SQLServerException: La conexión está cerrada. ] which will not be reported to listeners!

I'm not very big on reading Microsoft SQL Server error messages in Spanish, but it looks like connection to the server was lost. Either server was restarted or something happened in the network.