problem with email attachment

Hi All!

I am using FM SO_NEW_DOCUMENT_ATT_SEND_API1 to send a excel file as an attachment to a email address and I am facing the following problem.

After I receive the email along with excel attachment if i try to open the excel attachment I am getting an warning saying

" THIS FILE IS NOT IN A RECOGNIZABLE FORMAT"

but if i say okay I am getting the required ecxel data which i sent through email.

Why i am gettinmg this warning .Please advise

Regards

Praneeth