diff --git a/common/src/java/com/zimbra/common/service/ServiceException.java b/common/src/java/com/zimbra/common/service/ServiceException.java
index 9699bd2db62..5147b9aac2c 100644
--- a/common/src/java/com/zimbra/common/service/ServiceException.java
+++ b/common/src/java/com/zimbra/common/service/ServiceException.java
@@ -456,6 +456,15 @@ public static ServiceException UNSUPPORTED() {
         return new ServiceException("unsupported", UNSUPPORTED, RECEIVERS_FAULT);
     }
 
+    /**
+     * ServiceException in case wrong config provided by Sender
+     * @param msg
+     * @return
+     */
+    public static ServiceException UNSUPPORTED_CONFIG(String msg) {
+        return new ServiceException("unsupported: " + msg, UNSUPPORTED, SENDERS_FAULT);
+    }
+
     public static ServiceException FORBIDDEN(String str) {
         return new ServiceException("forbidden: " + str, FORBIDDEN, SENDERS_FAULT);
     }
diff --git a/store/src/java/com/zimbra/cs/store/StoreManager.java b/store/src/java/com/zimbra/cs/store/StoreManager.java
index cd63b8c99d9..1b9ca10688a 100644
--- a/store/src/java/com/zimbra/cs/store/StoreManager.java
+++ b/store/src/java/com/zimbra/cs/store/StoreManager.java
@@ -50,7 +50,6 @@ public static StoreManager getInstance(String className) {
                 if (sInstance != null) {
                     return sInstance;
                 }
-
                 try {
                     if (className != null && !className.equals("")) {
                         try {
@@ -69,12 +68,16 @@ public static StoreManager getInstance(String className) {
         return sInstance;
     }
 
+
+
     /**
      * Used for unit testing.
      */
     public static void setInstance(StoreManager instance) {
-        ZimbraLog.store.info("Setting StoreManager to " + instance.getClass().getName());
-        sInstance = instance;
+        synchronized (StoreManager.class) {
+            ZimbraLog.store.info("Setting StoreManager to " + instance.getClass().getName());
+            sInstance = instance;
+        }
     }
 
     public static int getDiskStreamingThreshold() throws ServiceException {