Product download page blank - More fun than it sounds

When clicking "Download Now" users are taken to a blank page, URL: /index.php?main_page=download&order=172&id=70 - so it seems it's not even getting to the URL forwarding, and there's no aliases in pub which seems to confirm this.

.htaccess is in place in both the download and pub folders and the file type is simply .pdf so the type shouldn't be an issue. pub has 777 permissions, download has 705 permissions. Attribute's download count is fine, attribute redirect is on. ZC v.1.3.9h

Last year it was working fine (my client doesn't use the download feature often) and now it's magically broken. I suspect the host (GoDaddy) upgraded the PHP version from 4 to 5 as there was a php.ini file but no php5.ini and the phpinfo states v5.2.17. I created the new php5.ini with the same info as 4:

register_globals = on
allow_url_fopen = off

expose_php = Off
max_input_time = 60
variables_order = "EGPCS"
extension_dir = ./
upload_tmp_dir = /tmp
precision = 12
SMTP = relay-hosting.secureserver.net
url_rewriter.tags = "a=href,area=href,frame=src,input=src,form=,fieldset="

[Zend]
zend_extension=/usr/local/zo/ZendExtensionManager.so
zend_extension=/usr/local/zo/4_3/ZendOptimizer.so

No change though.

Far as I can recall this setup has no plugins or customizations to zen cart code...

Any suggestions? I am stumped on this one.

Check out the blank-page FAQ: http://www.zen-cart.com/content.php?124-blank-page

Thanks for the link, I've gone through each item in the blank-page FAQ and didn't come up with anything.

The log only shows errors from when the layout was being customized after installation, there are no errors after the date where the file downloads were working correctly (last year).

The files could be downloaded fine before and now via FTP so it seems they are not corrupt. (Plus the URL for the download is incorrect so it's not getting to the files yet)

And strict error reporting gave me nada. It gave me the nice red box on all other pages saying it was on, but when coming to /index.php?main_page=download&order=172&id=72 it was still blank.

It seems like this should be something easy if it was working before, and if the PHP version was upgraded, it seems like a simple php5.ini fix or something like that. I wouldn't assume Zen Cart would have PHP4-only code that would stop working now that it's on php5 and I would expect some sort of error to generate in that case. I suppose it's worth checking into the pub URL and alias generation code just for kicks...

There were changes to Zen Cart 1.5.0 that were required for PHP 5.3 and some to 1.5.1 that are required for PHP 5.4. What version of PHP are you using for your 1.3.9h Zen Cart?

PHP version is 5.2.17

Sounds like your /includes/modules/pages/download/header_php.php file is missing or damaged.

Shouldn't be a PHP5 issue, unless your site has customized code or addons added to it that aren't compatible with PHP5. Zen Cart v1.3.9h itself should work fine with PHP 5.2

That'd be the one! Downloaded a fresh copy of the file, uploaded and all is well again. Thanks for the help guys!