Unable to generate excel attachment for large volume of data , using CL_BCS class

Dear Friends,

I am sending the report output as excel attachment in the mail ,with CL_BCS class functionality.When there are few records excel attachment is generating and subsequently mail is sent.

But here i am facing one issue,for large volume of data(More than 1000 records),excel attachment is not generating and unable to send the mail.

Please let me know the reason for this