impossible to accede to a file with fopen

With Matlab 2012b + simulink, I use a Matlab function to write data in a .txt file. Sometime, a problem to accede to the file occurs. The problem is that a window appears: title of the window is "Remote". The window contain the following text (in french): "Impossible to accede to the file "Elapsed_Real_Time.txt. Continue to try to communicate? YES/NO"

When the window appears, it stops the access to the file and the data is not written anymore.

The model was working with matlab 2007. Is it necessary to a code line to avoid the problem.

function Matlab_to_WM(u)
    coder.extrinsic('dlmwrite');
    coder.extrinsic('fopen');
    coder.extrinsic('fclose');

      fid=double(0);
      fid=fopen('D:\damien\Echange_donnees_System\Elapsed_Real_Time.txt', 'w');
      if fid ~= -1 && fid ~= 2
          dlmwrite('D:\damien\Echange_donnees_System\Elapsed_Real_Time.txt' , u , 'newline', 'pc');
      end
      fclose('all');
  end

Answer 1

[Iain]

Do not use fopen then try to use dlmwrite/csvwrite/etc.

[Damien DUDUYER]

I forgot to specify that the .txt file is read by an other software. The txt file is used for data exchange. That's why I check whith fopen if the file is accessible or not. Without using fopen, I will have an error when dmlwrite try to write the data in the same time that the other software have opened the file to read the data.