serial communication problem

Projects Programming
7

im guessing another rookie mistake:

More than one. First, the serial prints don't define what data you are printing. Second, the serial prints don't show where the data of interest starts and ends. Third, you didn't share the output with us.

Serial.println(readString);

would convey a LOT more information as:

Serial.print("Serial port data: [");
Serial.print(readString);
Serial.println("]");

One final problem is the String class. When you KNOW how much data is to be sent, using NULL terminated char arrays is far better. Quit using the String class crutch.