Exception : java.io.Writer.write(Unknown source)

Could some Java guru please help. I am using:
java version "1.6.0_16"
Java(TM) SE Runtime Environment (build 1.6.0_16-b01)
Java HotSpot(TM) Client VM (build 14.2-b01, mixed mode, sharing)

I have a simple command line driven program that outputs large amounts
of text into a simple text file. In the constructor, I have :
if(filename != null)
{
 try
 {
  outFile = new File(filename);
   if(!outFile.exists())
   {
    outFile.createNewFile();
  }
 if(outFile != null)
 {
    fileWriter = new FileWriter(outFile);
     if(fileWriter != null)
     {
             bufferedWriter = new
                           BufferedWriter(fileWriter);
        }
  }
}
catch(IOException ioe)
{
  System.out.println(" constructor IO exception");
  ioe.printStackTrace();
  System.exit(0);
}
}

In the main code body, I have functions that write output to text file
as:
bufferedWriter.write(<some_text>);

And then I frequently get the IO exception:
java.io.Writer.write(Unknown source)

Is this is a known Java bug, or is there something wrong in my code ?
Any hints, suggestions would be of great help - thanks in advance for
your help.