Cant use project and serial monitor

[jonjon0815]

Hi,` I am using this code

#include <BillValidator.h>
#include <CoinChanger.h>
#include <MDBSerial.h>

#define DEBUG true

MDBSerial mdb(1);
CoinChanger changer(mdb);
BillValidator validator(mdb);
UART uart;

int auswahl = 0;
int zahl = 0;

void setup() {
  Serial.begin(9600);
  Init_Muenzen();
  Init_Scheinleser();
  Init_DMC5();
  Init_Display();
  Init_Product();
}

void loop() {
  unsigned long change;
  changer.Update(change);
  validator.Update(change);
  delay(200);
  byte key = getKeyy();
  if(key != -1){
    
  }

}

void printDebug(String line){
  if(DEBUG){
    Serial.println(line);
  }
}

when I try to compile I get this error:

HardwareSerial0.cpp.o (symbol from plugin): In function `Serial':
(.text+0x0): multiple definition of `__vector_25'
libraries\ArduinoMDB-master\UART.cpp.o (symbol from plugin):(.text+0x0): first defined here
collect2.exe: error: ld returned 1 exit status
exit status 1

I can't get any further can you help me so that I can use MDB and USB Monitor?
It works fine without the USB serial monitor.