SD.exists

Hi!
I am having trouble getting my SD code working.

#include <SD.h>

const int chipSelect = 4;

int logNr = 1;
int n = 0;
String fileName = "/Ard/LOG";

void setup()
{
 // Open serial communications and wait for port to open:
  Serial.begin(9600);

  Serial.print("Initializing SD card...");
  // make sure that the default chip select pin is set to
  // output, even if you don't use it:
  pinMode(10, OUTPUT);
  
  // see if the card is present and can be initialized:
  if (!SD.begin(chipSelect)) {
    Serial.println("Card failed, or not present");
    // don't do anything more:
    return;
  }
  Serial.println("Card initialized.");
  
  Serial.print("Checking directory...");
  if (!SD.exists("/Ard")){
    SD.mkdir("/Ard");
  }
  Serial.println("Done");
  Serial.print("Setting up LOG file name...");
  String file = fileName + String(logNr) + ".txt";
  while(SD.exists(file)){
    logNr++;
    file = fileName + String(logNr) + ".txt";
  }
  
  fileName = file;
  String msg = " Done (" + fileName ")";
  Serial.println(msg);
}
SD_Log1.ino: In function 'void setup()':
SD_Log1:35: error: no matching function for call to 'SDClass::exists(String&)'
C:\Users\Michael Marne\Desktop\Arduino\arduino-1.0.5\libraries\SD/SD.h:77: note: candidates are: boolean SDClass::exists(char*)
SD_Log1:41: error: expected ',' or ';' before string constant
SD_Log1.ino: In function 'void loop()':
SD_Log1:54: error: no matching function for call to 'SDClass::open(String&, int)'
C:\Users\Michael Marne\Desktop\Arduino\arduino-1.0.5\libraries\SD/SD.h:74: note: candidates are: File SDClass::open(const char*, uint8_t)

I don't really know what to make of this error. What am I doing wrong?

What am I doing wrong?

Using the String class.

Is there some part of the error message saying that the SD methods don't support the String class that is all that difficult to understand?