Truncated files

I don't have the code I used right in front of me, so I'm sorry that I can't give specifics, but maybe someone may have an idea about this off the top of their head. I have a script that processes a form on my site where people can submit information and upload files. The files don't upload to a directory; they're attached to an e-mail and sent along with whatever information they give. However, when the e-mail reaches me and I look, the file size is down to 646 bytes or so (from a 300kb file) and the file is unreadable. Any ideas? Thanks, Jason