This means that the size of the message, including all text and attachments, is too big to be received . You should tell the sender to reduce the size of the message, or to split the email into smaller parts and resend it.
Or you can suggest that the sender upload the attachment to your SkyDrive. You’ll need to share a SkyDrive folder with the sender. Ensure you check “Recipients can edit” when you do so, to allow the person to upload files.