problem sd card

someone Know why this code not works? thanks.

     String call = "llamadauno";
     if (SD.exists(call))
     {
         digitalWrite(led,HIGH);
     }

mistake: no matching function for call to 'SDClass::exists(String&)'

The argument to exists() must be type char*, not String.

File names must be short 8.3 format. "llamadauno" is too long.

The maximum number of characters before the period is 8.

http://arduino.cc/forum/index.php?topic=84378.0 and http://stackoverflow.com/questions/14467568/arduino-opening-sd-filename-as-string

btw the first two hits on google searching for "SD.exists(call) SDClass::exists(String&)"