Sending attachments in email from sandbox app

I have build an application which uses the email widget tot sent mail with a PDF as attachment to a list of mail adresses, In local deployment this works but when I deploy the application to the sandbox the mail is sent but without the attachment. Does anyone know what the reason can be?
1 answers

Perhaps a too straight forward soluation, but did you upload the PDF in the Sandbox as well? The Sandbox uses his own database.