diff --git a/src/java/davmailmessages.properties b/src/java/davmailmessages.properties
index 3570fea1..4eea4566 100644
--- a/src/java/davmailmessages.properties
+++ b/src/java/davmailmessages.properties
@@ -15,7 +15,7 @@ EXCEPTION_INVALID_CREDENTIALS=Invalid credentials
 EXCEPTION_INVALID_DATE=Invalid date: {0}
 EXCEPTION_INVALID_DATES=Invalid dates: {0}
 EXCEPTION_INVALID_FOLDER_URL=Invalid folder URL: {0}
-EXCEPTION_INVALID_HEADER=Invalid header: {0}
+EXCEPTION_INVALID_HEADER=Invalid header: {0}, HTTPS connection to an HTTP listener ? 
 EXCEPTION_INVALID_ICS_LINE=Invalid ICS line: {0}
 EXCEPTION_INVALID_KEEPALIVE=Invalid Keep-Alive: {0}
 EXCEPTION_INVALID_MAIL_PATH=Invalid mail path: {0}
diff --git a/src/java/davmailmessages_fr.properties b/src/java/davmailmessages_fr.properties
index d1508d79..224f92e1 100644
--- a/src/java/davmailmessages_fr.properties
+++ b/src/java/davmailmessages_fr.properties
@@ -14,7 +14,7 @@ EXCEPTION_INVALID_CREDENTIALS=Identifiant ou mot de passe invalide
 EXCEPTION_INVALID_DATE=Date invalide {0}
 EXCEPTION_INVALID_DATES=Dates invalides : {0}
 EXCEPTION_INVALID_FOLDER_URL=URL du dossier invalide : {0}
-EXCEPTION_INVALID_HEADER=Entête invalide : {0}
+EXCEPTION_INVALID_HEADER=Entête invalide : {0}, connexion HTTPS sur le service HTTP ?
 EXCEPTION_INVALID_ICS_LINE=Ligne ICS invalide : {0}
 EXCEPTION_INVALID_KEEPALIVE=Keep-Alive invalide : {0}
 EXCEPTION_INVALID_MAIL_PATH=Chemin de messagerie invalide : {0}