Grove Multichannel Gas Sensor doesn't work with Arduino MKR wifi 1010

I have a problem with my Grove Multichannel Gas Sensor. When I try to take gases concentrations from my sensor it returns in serial monitor “invalid ppm” (<0). When I use my Arduino Uno it works normally. It gives me problems only with MKR. I’m not an exepert but I didn’t think it will be so difficult. This is the code:

#include <Wire.h>
#include "MutichannelGasSensor.h"

void setup()
{
  Serial.begin(115200); // start for output
  while (!SerialUSB) {

  }
  Serial.println("power on!");
  gas.begin(0x04);//the default I2C address of the slave is 0x04
  gas.powerOn();
  Serial.print("Firmware Version = ");
  Serial.println(gas.getVersion());
}

void loop()
{
  float c;

  c = -gas.measure_NH3();
  Serial.print("The concentration of NH3 is ");
  if (c >= 0) Serial.print(c);
  else Serial.print("invalid");
  Serial.println(" ppm");

  c = -gas.measure_CO();
  Serial.print("The concentration of CO is ");
  if (c >= 0) Serial.print(c);
  else Serial.print("invalid");
  Serial.println(" ppm");

  c = -gas.measure_NO2();
  Serial.print("The concentration of NO2 is ");
  if (c >= 0) Serial.print(c);
  else Serial.print("invalid");
  Serial.println(" ppm");

  c = -gas.measure_C3H8();
  Serial.print("The concentration of C3H8 is ");
  if (c >= 0) Serial.print(c);
  else Serial.print("invalid");
  Serial.println(" ppm");

  c = -gas.measure_C4H10();
  Serial.print("The concentration of C4H10 is ");
  if (c >= 0) Serial.print(c);
  else Serial.print("invalid");
  Serial.println(" ppm");

  c = -gas.measure_CH4();
  Serial.print("The concentration of CH4 is ");
  if (c >= 0) Serial.print(c);
  else Serial.print("invalid");
  Serial.println(" ppm");

  c = -gas.measure_H2();
  Serial.print("The concentration of H2 is ");
  if (c >= 0) Serial.print(c);
  else Serial.print("invalid");
  Serial.println(" ppm");

  c = -gas.measure_C2H5OH();
  Serial.print("The concentration of C2H5OH is ");
  if (c >= 0) Serial.print(c);
  else Serial.print("invalid");
  Serial.println(" ppm");

  delay(1000);
  Serial.println("...");
}

why is there a "-" in that line?

The example code(http://wiki.seeedstudio.com/Grove-Multichannel_Gas_Sensor/) doesn't...

c = -gas.measure_CO();[\code]