Index: lams_common/src/java/org/lamsfoundation/lams/web/session/SessionManager.java
===================================================================
diff -u -r563e90bc56ef37e24ad9cdc801e3fe6350e19932 -rc7b64c1297f46800d132a6db434955b3a75ff34b
--- lams_common/src/java/org/lamsfoundation/lams/web/session/SessionManager.java	(.../SessionManager.java)	(revision 563e90bc56ef37e24ad9cdc801e3fe6350e19932)
+++ lams_common/src/java/org/lamsfoundation/lams/web/session/SessionManager.java	(.../SessionManager.java)	(revision c7b64c1297f46800d132a6db434955b3a75ff34b)
@@ -41,6 +41,7 @@
 import org.lamsfoundation.lams.usermanagement.dto.UserDTO;
 import org.lamsfoundation.lams.util.DateUtil;
 import org.lamsfoundation.lams.web.util.AttributeNames;
+import org.springframework.http.MediaType;
 
 public class SessionManager {
     private static Logger log = Logger.getLogger(SessionManager.class);
@@ -90,6 +91,13 @@
 	    HttpSession existingSession = loginMapping.get(login);
 	    // check if it's a different session and if so, which one is newer
 	    if (existingSession != null && !existingSession.getId().equals(sessionId)) {
+		String acceptHeader = request.getHeader("Accept");
+		if (MediaType.TEXT_EVENT_STREAM_VALUE.equals(acceptHeader)) {
+		    throw new IllegalArgumentException(
+			    "When fetching Event Stream data error while trying to use session ID \"" + sessionId
+				    + "\" when another one is in use \"" + existingSession.getId() + "\"");
+		}
+
 		try {
 		    // invalidate the other session
 		    existingSession.invalidate();
Index: lams_common/src/java/org/lamsfoundation/lams/web/session/SystemSessionFilter.java
===================================================================
diff -u -r563e90bc56ef37e24ad9cdc801e3fe6350e19932 -rc7b64c1297f46800d132a6db434955b3a75ff34b
--- lams_common/src/java/org/lamsfoundation/lams/web/session/SystemSessionFilter.java	(.../SystemSessionFilter.java)	(revision 563e90bc56ef37e24ad9cdc801e3fe6350e19932)
+++ lams_common/src/java/org/lamsfoundation/lams/web/session/SystemSessionFilter.java	(.../SystemSessionFilter.java)	(revision c7b64c1297f46800d132a6db434955b3a75ff34b)
@@ -69,13 +69,14 @@
 	    chain.doFilter(request, response);
 	    return;
 	}
-
-	HttpSession session = SessionManager.startSession(httpRequest);
-	// do following part of chain
+	
+	HttpSession session = null;
 	try {
+	    session = SessionManager.startSession(httpRequest);
+	    // do following part of chain
 	    chain.doFilter(request, response);
 	} catch (NestedServletException e) {
-	    if (e.getCause() instanceof IllegalStateException) {
+	    if (e.getCause() instanceof IllegalStateException && session != null) {
 		// There seems to be a problem with Infinispan session invalidation.
 		// Until we upgrade WildFly we need to keep these safety measures.
 		String sessionId = session.getId();
@@ -84,6 +85,8 @@
 	    } else {
 		throw e;
 	    }
+	} catch (IllegalArgumentException e) {
+	    log.warn("Error while creating session: " + e.getMessage());
 	} finally {
 	    SessionManager.endSession();
 	}