         let firstChar = "X"
         var data : NSData! = firstChar.dataUsingEncoding(NSUTF8StringEncoding)
         
-        return data.writeToURL(self.url, atomically: true)
+        // TRUE if the operation succeeds, otherwise FALSE.
+        return data.writeToURL(self.url, options: .DataWritingAtomic , error: &self.error)
     }
     
     // override in subclasses
-    // This method is called only if the file is new
+    // This method is called only if the file is new and no error is occurred
     // The intension is to write the datablock number 0
     func initStore() {
         

    let blockSize = sizeof(H) + sizeof(D)  // test as CUnsignedLongLong
    
    public var error: NSError?  // readonly?
    
    var url: NSURL!
    var fileHandle: NSFileHandle!

    }

    // override in subclasses
    // This method is called only if the store is NOT new and no error is occurred
    // The intension is to scan an existing store and extract relevant data
    // - The default implementation call "readUnusedDataSegments" starting with block 1 (one)
    func readStoreConfiguration() {
