Robin2:
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
Sorry...
The Shield is completely on the Uno, so yes every pin is "occupied".
If you mean the analog Pins 0 and 1 on the shield (or the Uno) then the answer is also yes, they are used for the linefinder.
Is it possible that there's suddenly a problem with that although I didn't switch the pins at all??
I hope that answer is sufficient now... English's not my mother language...
E99