DB connection problem : Connection handle has been closed and is unusable

Dear all,
I have all the time this error when 2 or more users work with the workflow.
Any idea?

Thanks in advance,
philippe

[com.adobe.idp.storeprovider.jdbc.DBStatement] errorCode:12290 errorCodeHEX:0x3002 message:execute query failure(select * from (select /*+ FIRST_ROWS */ * from EDCCREDENTIALENTITY where (EDCCREDENTIALENTITY.canonicalName = ?)) where rownum < 2) chainedException:java.sql.SQLException: Connection handle has been closed and is unusablechainedExceptionMessage:Connection handle has been closed and is unusable chainedException trace:java.sql.SQLException: Connection handle has been closed and is unusable
at org.jboss.resource.adapter.jdbc.WrappedConnection.checkStatus(Wrapped Connection.java:526)
at org.jboss.resource.adapter.jdbc.WrappedConnection.checkTransaction(Wr appedConnection.java:513)
at org.jboss.resource.adapter.jdbc.WrappedConnection.prepareStatement(Wr appedConnection.java:184)
at com.adobe.idp.storeprovider.jdbc.DBStatement.executeQuery(DBStatement .java:295)
at com.adobe.idp.storeprovider.jdbc.DBStoreProvider.retrieveAll(DBStoreP rovider.java:2048)
at com.adobe.idp.storeprovider.jdbc.DBStoreProvider.retrieve(DBStoreProv ider.java:1757)
at com.adobe.idp.storeprovider.jdbc.DBStoreProvider.retrieve(DBStoreProv ider.java:1804)
at com.adobe.idp.storeprovider.spi.StoreProvider.retrieve(StoreProvider. java:146)
at com.adobe.idp.um.credential.CredentialHelper.findCredentialEntityKeyD ata(CredentialHelper.java:73)
at com.adobe.idp.um.credential.CredentialClient.getCredentials(Credentia lClient.java:92)
at com.adobe.workspace.AssemblerUtility.getAdminContext(AssemblerUtility .java:517)
at com.adobe.workspace.users.Authentication.doSSO(Authentication.java:29 4)
at com.adobe.workspace.users.Authentication.servletCheckLogin(Authentica tion.java:234)
at com.adobe.workspace.users.AuthenticationServlet.doGet(AuthenticationS ervlet.java:53)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:697)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:810)
at sun.reflect.GeneratedMethodAccessor280.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAcces sorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:243 )
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAsPrivileged(Subject.java:517)
at org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:2 75)
at org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil. java:161)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(Appl icationFilterChain.java:245)
at org.apache.catalina.core.ApplicationFilterChain.access$000(Applicatio nFilterChain.java:50)
at org.apache.catalina.core.ApplicationFilterChain$1.run(ApplicationFilt erChain.java:156)
at java.security.AccessController.doPrivileged(Native Method)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationF ilterChain.java:152)
at com.adobe.workspace.events.RemoteEventClientLifeCycle.doFilter(Remote EventClientLifeCycle.java:126)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl. java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAcces sorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:243 )
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAsPrivileged(Subject.java:517)
at org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:2 75)
at org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil. java:217)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(Appl icationFilterChain.java:197)
at org.apache.catalina.core.ApplicationFilterChain.access