Files downloaded from my site are erroring out

I offer photoshop designs to photographers that they can download directly from my online shopping cart (xCart installed on my VPS server at Dreamhost). I just started to branch out into books, which are much larger files, and am now having problems getting the files to download.

When I try to download a file, it immediately creates a zip.cpgz file. I talked with customer service at Dreamhost and they said it is indeed erroring out, that it’s saying the file is not there. However, if I open up my FTP and navigate to the zipped file I have uploaded there, it shows that it is indeed there and that it’s 650mb in size.

The Dreamhost customer service tech said that it looks like it’s trying to create a custom URL to the file and he thought maybe that’s where I’m having issues, but all of my other products are uploaded in the same manner and can be downloaded fine. I’m assuming it has something to do with the size of the file.

Any suggestions as to what I can look for or trouble shoot to get these new, larger files downloaded?

In what format is the file stored on the server?