Thanks to @s1lv3r and @GhostToast for their useful advice in chat I have located the issue.

As stated in my original question asked above, I stated that I have tested both FAST-CGI and MOD-PHP, were both continuing to replicate the same error.

As stated in chat I have tested on both Ubuntu 12.04 and CentOS 5.9 dedicated servers.

The chat message by @s1lv3r is ultimately the one who sparked the idea of testing PHP-FPM as well... and would you look at that? PHP-FPM solved the mystery!

I have tested numerous times on both Ubuntu 12.04 and CentOS 5.9 along with no plugins enabled, with plugins enabled, with stock theme enabled, and with custom theme enabled. It most definitely uploaded every image, however small or large -- without error.

So once again in-case you didn't catch it earlier. If you're experiencing similar symptoms with your WordPress multi-site. Try enabling PHP-FPM on your server, or as stated in chat by @s1lv3r You could try chmodding your uploads directory to 777 if you're using FAST-CGI.

Enabling PHP-FPM solved this particular issue with WordPress multi-site causing an HTTP error upon image upload.

BoF EDIT 10/20/2016

If you're getting HTTP Errors with WordPress Multisite, consider the way your installation is configured.

There are two options for WordPress Multisite:

1. Subdirectory installtion
2. Subdomain installtion

I've been managing a network of sites all using TLDs on a "subdirectory" installation. They worked just fine forever. All of the sudden they started failing during file uploads with "HTTP Error".

The problem was only happening in WordPress and the problem is HTTP. So there's something which WordPress AND Apache both relied on. The only common link is .htaccess.

If you look on the WordPress Codex :: .htaccess and Mod Rewrite The rewrite rules are actually very different depending on the type of installation you have configured for Multisite.

I replaced the rewrite rules for a "subdirectory" installation with the appropriate rewrite rules for a "subdomain" installation. I then also updated wp-config.php to change define('SUBDOMAIN_INSTALL', false); to this define('SUBDOMAIN_INSTALL', true);

BOOM! Problem solved. No more HTTP Error on file uploads in WordPress Multisite using TLDs for each site in the network.

EoF EDIT 10/20/2016

Thanks to @s1lv3r and @GhostToast for their useful advice in chat I have located the issue.

As stated in my original question asked above, I stated that I have tested both FAST-CGI and MOD-PHP, were both continuing to replicate the same error.

As stated in chat I have tested on both Ubuntu 12.04 and CentOS 5.9 dedicated servers.

The chat message by @s1lv3r is ultimately the one who sparked the idea of testing PHP-FPM as well... and would you look at that? PHP-FPM solved the mystery!

I have tested numerous times on both Ubuntu 12.04 and CentOS 5.9 along with no plugins enabled, with plugins enabled, with stock theme enabled, and with custom theme enabled. It most definitely uploaded every image, however small or large -- without error.

So once again in-case you didn't catch it earlier. If you're experiencing similar symptoms with your WordPress multi-site. Try enabling PHP-FPM on your server, or as stated in chat by @s1lv3r You could try chmodding your uploads directory to 777 if you're using FAST-CGI.

Enabling PHP-FPM solved this particular issue with WordPress multi-site causing an HTTP error upon image upload.

BoF EDIT 10/20/2016

If you're getting HTTP Errors with WordPress Multisite, consider the way your installation is configured.

There are two options for WordPress Multisite:

1. Subdirectory installtion
2. Subdomain installtion

I've been managing a network of sites all using TLDs on a "subdirectory" installation. They worked just fine forever. All of the sudden they started failing during file uploads with "HTTP Error".

The problem was only happening in WordPress and the problem is HTTP. So there's something which WordPress AND Apache both relied on. The only common link is .htaccess.

If you look on the WordPress Codex :: .htaccess and Mod Rewrite The rewrite rules are actually very different depending on the type of installation you have configured for Multisite.

I replaced the rewrite rules for a "subdirectory" installation with the appropriate rewrite rules for a "subdomain" installation. I then also updated wp-config.php to change define('SUBDOMAIN_INSTALL', false); to this define('SUBDOMAIN_INSTALL', true);

BOOM! Problem solved. No more HTTP Error on file uploads in WordPress Multisite using TLDs for each site in the network.

EoF EDIT 10/20/2016

Thanks to @s1lv3r and @GhostToast for their useful advice in chat I have located the issue.

As stated in my original question asked above, I stated that I have tested both FAST-CGI and MOD-PHP, were both continuing to replicate the same error.

As stated in chat I have tested on both Ubuntu 12.04 and CentOS 5.9 dedicated servers.

The chat message by @s1lv3r is ultimately the one who sparked the idea of testing PHP-FPM as well... and would you look at that? PHP-FPM solved the mystery!

I have tested numerous times on both Ubuntu 12.04 and CentOS 5.9 along with no plugins enabled, with plugins enabled, with stock theme enabled, and with custom theme enabled. It most definitely uploaded every image, however small or large -- without error.

So once again in-case you didn't catch it earlier. If you're experiencing similar symptoms with your WordPress multi-site. Try enabling PHP-FPM on your server, or as stated in chat by @s1lv3r You could try chmodding your uploads directory to 777 if you're using FAST-CGI.

Enabling PHP-FPM solved this particular issue with WordPress multi-site causing an HTTP error upon image upload.

Thanks to @s1lv3r and @GhostToast for their useful advice in chat I have located the issue.

As stated in my original question asked above, I stated that I have tested both FAST-CGI and MOD-PHP, were both continuing to replicate the same error.

As stated in chat I have tested on both Ubuntu 12.04 and CentOS 5.9 dedicated servers.

The chat message by @s1lv3r is ultimately the one who sparked the idea of testing PHP-FPM as well... and would you look at that? PHP-FPM solved the mystery!

I have tested numerous times on both Ubuntu 12.04 and CentOS 5.9 along with no plugins enabled, with plugins enabled, with stock theme enabled, and with custom theme enabled. It most definitely uploaded every image, however small or large -- without error.

So once again in-case you didn't catch it earlier. If you're experiencing similar symptoms with your WordPress multi-site. Try enabling PHP-FPM on your server, or as stated in chat by @s1lv3r You could try chmodding your uploads directory to 777 if you're using FAST-CGI.

Enabling PHP-FPM solved this particular issue with WordPress multi-site causing an HTTP error upon image upload.

BoF EDIT 10/20/2016

If you're getting HTTP Errors with WordPress Multisite, consider the way your installation is configured.

There are two options for WordPress Multisite:

1. Subdirectory installtion
2. Subdomain installtion

I've been managing a network of sites all using TLDs on a "subdirectory" installation. They worked just fine forever. All of the sudden they started failing during file uploads with "HTTP Error".

The problem was only happening in WordPress and the problem is HTTP. So there's something which WordPress AND Apache both relied on. The only common link is .htaccess.

If you look on the WordPress Codex :: .htaccess and Mod Rewrite The rewrite rules are actually very different depending on the type of installation you have configured for Multisite.

I replaced the rewrite rules for a "subdirectory" installation with the appropriate rewrite rules for a "subdomain" installation. I then also updated wp-config.php to change define('SUBDOMAIN_INSTALL', false); to this define('SUBDOMAIN_INSTALL', true);

BOOM! Problem solved. No more HTTP Error on file uploads in WordPress Multisite using TLDs for each site in the network.

EoF EDIT 10/20/2016