Excel attachment with SO_DOCUMENT_SEND_API1

Hello Everyone,

I am using SO_DOCUMENT_SEND_API1 for sending mail.

It works well with text attachment.

Whereas with excel attachment:

The fn module for sending mail ‘SO_DOCUMENT_SEND_API1’ gives return code zero.

The excel attachment mail can be seen in transaction SOST. But its process fails stating that it cannot be converted.

(Message : Message cannot be processed as it cannot be converted)

Can anyone suggest me what might be wrong ??