not able to open file in XLS format of email attachement, error 'it is not recognized format'

Hi,

I have to send data in excel format using attachment, I have code accordingly,but when I open the attachement that came in the mail box,and save it, it shows the error message that 'it is not recognized format'. so how can i resolve this issue?

Currently I am using the Office 2003 ,and to open office 2007 file , i have installed the office Compability pack .

So, please let me know that how can i solve this problem?

Thanks,

Dhaval