help~download attachment

Hi,

I have a question regarding downloading the attachment on the server.
I upload some files to tciket, for example, and then I try to download and open it.
The pdf file can be opened normally, but jpg, doc, xls, xlsx, ppt can't.
The languages written in the file are Chinese and English.
Microsoft Word said I need to have a converting tool/plugin to convert it. The content becomes unreadable, many "? ? ? ?? " in the file
Excel will let me open the xls, but the content is also "? ? ". for xlsx files, it said format or extension is invalid.
On the server side, I checked the files. The files are displayed ok.

I tried to do the same on your demo system (V2.0.1). But everything seems fine.
My current system is based on V1.5.5 and I've already done some customization for it. It would be very difficult to upgrade the system.
I diffed the download.php, except the new feature documentation code part you introduced in v2.0.0, no other differences between v1.5.5 and v2.0.1.
Can you help point out what might be missing in my system? Will the encode/decode will be the key issue to it? How can I solve this problem?
Thanks in advance.


Best Regards,
Selina