einfallslose99:
I have the Wifi-Shield ESP8266 on the Arduino.
You are not answering questions with sufficient precision.
I asked "Have you anything connected to pins 0 and 1 on the Uno?"
If your ESP8266 is connected to pins 0 and 1 that is probably what is preventing the code from uploading because pins 0 and 1 are used by Serial as part of the program upload process.
...R