[otrs] Problem with attach file in otrs 2.4.9

i am working on OTRS 2.4.9, and right now i'm trying to implement the file attachment.. here's my problem: after I attach a file to a ticket (successfully; because I can see it in Article_Attachment table in the DB) and send it, when I want to check the ticket and download the attached file, the content of the downloaded file is corrupted... for example, if I attach a pdf file, the files is like a clean sheet when I download it... or if I attach an Excel file, I can't check the content of the file and there's message about the file being corrupted. any advice would be appreciated. thx.