Photos downloaded in zip file from favorites all corrupt

[stressball]

Here's my problem:
I select photos and add them to my favorites.
I view my favorites
I click on "Download as Zip file"
The file downloads just fine
I open it up and nothing will unzip it because all the programs I've tried using say the files are corrupt. (programs tried: winRAR, WinZip, and Windows Compressed File Wizard (comes with Windows))

Now, I have this same version of Coppermine (1410) installed on two different servers at my office.  They both have the same mods, so I have ensured they are the exact same (except for the number of pictures stored on them).  One of them is my test server, the other is production.  There are only about 30 photos on this test server, whereas on the production server there are about 2200.  My test server can download its favorites just fine, without any corrupted files. I have tested many different number of photos, just to be certain. On the production server, the photos display perfectly, and right-clicking and saving the photo will save it perfectly and it is viewable and not corrupt when viewed on my local machine after download.

Other helpful information: the test server runs on Windows, the production on Linux. I cannot include links to these because they are both internal sites (intranet).

Any ideas as to what's causing this? Thanks for the help.

[stressball]

About 20 minutes after I posted this, a light went on over my head. I am doing some more research into this matter, and if I'm right, I'll post my solution. If not, I'll come back crying for help.

[stressball]

And the answer was: ZLib was not enabled in my installation of PHP5.2. *hits head against wall*

You can mark this as solved or whatever now. Thanks.