File Permissions problem

I have an array which I have to write in an excel spreadsheet. I am using an 'a+' permission but not able to reopen the file with editable permissions.

This is the piece of code which I am using:

pause on;
File_ID_2=fopen(Excel_sheet_name,'a+');
while File_ID_2 == -1
    fprintf('Close the file and then press any key to continue.\n');
    pause;
    File_ID_2=fopen(Excel_sheet_name,'a+');
end
fclose(File_ID_2);
xlswrite(Excel_sheet_name,coeffvalues,Worksheet_name_optim,range_write);
pause off;

Thanks!

[Geoff]

Wow, I just commented on your _other_ question. Moments later, you deleted that question and posted the same question again. Oh well, never mind.