Getting Error when opening excel file

Jun 22, 2011 at 9:41 PM

Excel cannont open the file 'myfilename' because the file format or file extension is not valid.  Verify that the file has not been corrupted and that the file extension matches the format of the file.

 

I get this intermittently when i generate a phpexcel file.  I'm using textpad as my text editor.  Any ideas?? We are using version    1.7.5 of PHPExcel