2003 Skoda Other Fixed New Engine On Scoda Octavia After Replacement Local

I fixed a new engine on my scoda octavia after the replacement of new engine my local technician ask me to on the ignition when I on the ignition the engine sound cool but when I race the accelerator a message was showing on my dashbord STOP ENGINE SERVICE MANUAL OIL PRESS I just change the oil and oil filter of the new engine when ever I move at a low speed the error message will disappear but I move at high speed the error message will appear what is the problem