Opening Multiple SD Files on Due ?

Other Hardware Storage
1

There have been other posts in the past about opening multiple (>2?) SD files but I havn't found an answer.

I'm finding that I can't open more than 2 files even after closing 2 ? Is there something missing I have to do or is this a limitation of the SD library ?, are there any other SD library options ?

#include <SD.h>
#include <SPI.h>

void setup(){

  File testFile1;
  File testFile2;
  File testFile3;
  File testFile4;

  Serial.begin(9600);
  
  Serial.print("Initializing SD card...");
  if (!SD.begin(4)) {
    Serial.println(" failed!");
    while(true);
  }
  Serial.println(" done");

  testFile1 = SD.open("test1.txt");
  if (!testFile1) Serial.println("error opening test1");
  else Serial.println("test1 open");

  testFile1.close();
  Serial.println("test1 closed");

  testFile2 = SD.open("test2.txt");
  if (!testFile2) Serial.println("error opening test2");
  else Serial.println("test2 open");

  testFile2.close();

  Serial.println("test2 closed");

  testFile2 = SD.open("test3.txt");
  if (!testFile3) Serial.println("error opening test3");
  else Serial.println("test3 open");

  testFile2 = SD.open("test4.txt");
  if (!testFile4) Serial.println("error opening test4");
  else Serial.println("test4 open");

 while(true);
}

void loop(){

}