Motor Shield and Attachinterrupt, little interference problem

Projects General Guidance
5

please spent some time to get proper layout - CTRL-T does help you

#include <SPI.h>
#include <Ethernet.h>

byte mac[] = { 
  0x90, 0xA2, 0xDA, 0x0E, 0xCE, 0xA1 }; //physical mac address
byte ip[] = { 
  192, 168, 0, 2 }; // ip in lan
byte gateway[] = { 
  192, 168, 0, 1 }; // internet access via router
byte subnet[] = { 
  255, 255, 255, 0 }; //subnet mask
EthernetServer server(80); //server port

String readString; 

//////////////////////
int switchhh = 2;
int pwm = 5;
int dir = 7;
int valswitch = 0;

void setup()
{
  //Setup Channel A from Motor shield
  pinMode(pwm, OUTPUT); //Initiates Motor Channel A pin
  pinMode(dir, OUTPUT); //Initiates Brake Channel A pin
  //Start Ethernet
  Ethernet.begin(mac, ip, gateway, gateway, subnet);
  server.begin();
  //enable serial data print 
  Serial.begin(9600); 
  Serial.println("server multi pin button test 1.0"); // so I can keep track of what is loaded

  attachInterrupt(1, motor_stop, RISING);
}


void loop()
{
  // Create a client connection
  EthernetClient client = server.available();
  if (client) 
  {
    while (client.connected()) 
    {
      if (client.available()) 
      {
        char c = client.read();

        //read char by char HTTP request
        if (readString.length() < 100) 
        {
          //store characters to string 
          readString += c; 
          //Serial.print(c);
        } 

        //if HTTP request has ended
        if (c == '\n') 
        {
          ///////////////
          Serial.println(readString); //print to serial monitor for debuging 

            client.println("HTTP/1.1 200 OK"); //send new page
          client.println("Content-Type: text/html");
          client.println("");

          client.println("<HTML><HEAD><TITLE>Projet d'&eacute;tude : ARDUINO et Contr&ocirc;le de panneau solaire</TITLE></HEAD>");
          client.println("<BODY>");
          client.println("<H3>Projet d'&eacute;tude : ARDUINO et Contr&ocircle de panneau solaire</H3>");
          // DIY buttons
          client.println("<a href=/?up2 >Monter</a> <a href=/?down3 >Descendre</a> <a href=/?stop4 >STOP</a>"); 
          client.println("</BODY></HTML>");
          delay(1);
          //stopping client
          client.stop();

          ///////////////////// control arduino pin
          if(readString.indexOf('2') > 0)//checks for 2 MONTER
          {
            Serial.println("Bouton monter appuyer !!");
            digitalWrite(dir, HIGH);
            analogWrite(pwm, 255); 
            delay(3000);
            m_stop(); 
            Serial.println("Bouton monter appuyer !!  FIN BOUCLE");
          }
          if(readString.indexOf('3') > 0)//checks for 3 DESCENDRE
          {
            Serial.println("Bouton descendre appuyer !!");
            digitalWrite(dir, LOW);
            analogWrite(pwm, 255); 
          }
          if(readString.indexOf('4') > 0)//checks for 3 STOP
          {
            Serial.println("Bouton STOP appuyer !!");
            m_stop(); 
            Serial.println("Bouton STOP appuyer !!  FIN BOUCLE");
          }
          valswitch = digitalRead(switchhh);
          if (valswitch == HIGH)
          {
            //clearing string for next read
            readString="";
          } 
        }
      }
    }
  }
}

void motor_stop()
{
  Serial.println("motor_stop begin");
  m_stop();
  Serial.println("motor_stop end");
}

void m_stop()
{
  Serial.println("m_stop start");
  digitalWrite(pwm, 0);
  Serial.println("m_stop end");
}

and please use only comments when in sync with the code >>> if(readString.indexOf('4') > 0)//checks for 3 STOP

quick code review shows no direct errors. Are you running out of RAM?