serial port cange after post data from IDE

Hi, i've a problem with the serial port comunication, i use Arduino IDE on Ubuntu 15, when i try to send the first value for moving an servo motor the comunication work well but when i try to send the second value the IDE return an error of comunication and i'm forced to change the port... :frowning: what can i do??

Thank and sorry for my English....

#include <Servo.h>

 Servo servoMotor1;
 
 int grad = 0;
 //int gradMin=0;
 //int gradMax=180;
 
 int servoPin1 = 11;
 
 
 void setup() {
   servoMotor1.attach(servoPin1);
   
   Serial.begin(9600);
 } 
 
 void loop()
 {
   grad = Serial.read();
   Serial.println("Gradi: " + grad);
 
    
   servoMotor1.write( grad );
   delay(15);
 }