diff --git a/src/main/java/org/gcube/accounting/aggregator/persistence/CouchBaseConnector.java b/src/main/java/org/gcube/accounting/aggregator/persistence/CouchBaseConnector.java
index 87c8ab8..564effc 100644
--- a/src/main/java/org/gcube/accounting/aggregator/persistence/CouchBaseConnector.java
+++ b/src/main/java/org/gcube/accounting/aggregator/persistence/CouchBaseConnector.java
@@ -85,7 +85,7 @@ public class CouchBaseConnector {
 	protected Map<String,Bucket> connectionMap;
 	protected Map<String, Class<? extends Record>> recordTypeMap;
 	
-	public static CouchBaseConnector getInstance() throws Exception{
+	public synchronized static CouchBaseConnector getInstance() throws Exception{
 		if(couchBaseConnector==null){
 			couchBaseConnector = new CouchBaseConnector();
 		}
@@ -333,7 +333,7 @@ public class CouchBaseConnector {
 		List<N1qlQueryRow> rows = result.allRows();
 		
 		if(rows.size()>1){
-			String error = String.format("More than one Document found for query %. This is really strange and should not occur. Please contact the Administrator.", statement.toString());
+			String error = String.format("More than one Document found for query %s. This is really strange and should not occur. Please contact the Administrator.", statement.toString());
 			logger.error(error);
 			throw new Exception(error);
 		}