diff --git a/openbis/source/java/ch/systemsx/cisd/openbis/generic/client/web/server/AbstractClientService.java b/openbis/source/java/ch/systemsx/cisd/openbis/generic/client/web/server/AbstractClientService.java
index 6b5ae6312a7cdf400f0f7d054d9f3ec476f8b931..7a4af918ea47a57d592d1ab408f2507b6bae8d5c 100644
--- a/openbis/source/java/ch/systemsx/cisd/openbis/generic/client/web/server/AbstractClientService.java
+++ b/openbis/source/java/ch/systemsx/cisd/openbis/generic/client/web/server/AbstractClientService.java
@@ -319,6 +319,11 @@ public abstract class AbstractClientService implements IClientService,
         }
         if (sessionToken == null)
         {
+            String sessionId = (httpSession != null) ? httpSession.getId() : null;
+            String logMessage =
+                    String.format("Unable to find session token in session [%s], sessionId=[%s]",
+                            httpSession, sessionId);
+            operationLog.info(logMessage);
             throw new InvalidSessionException("Session expired. Please login again.");
         }
         return sessionToken;