If you're an iPhone jailbreaker, you're probably already familiar with TinyUmbrella, the versatile desktop application that can save your SHSH blogs, put your iOS device into and out of recovery mode, and run it's own TSS Server to convinces downgrades and restores that they're talking to Apple's servers instead of your own. It's a great tool and can easily be considered the iOS hackers swiss army knife.
That is, when it works.
If you've ever encountered the error "Cannot Start TSS Service DO NOT TRY RESTORING YOUR DEVICE!!! httpd(PID:4463) must be killed!!" you probably know what I mean. Your PID (process ID) probably differs, but if you're seeing this error on your Mac then some other service is preventing TinyUmbrella from successfully spoofing Apple's server address (gs.apple.com).
The fix is simple, once you know what the problem is. At first pass, I tried to kill that process by opening Activity Monitor (Applications > Utilities > Activity Monitor) and killing the process that matched the PID. Even if I killed every process labeled httpd prior to launching TinyUmbrella, the service software would still bark at me because the processes had re-spawned themselves.
A little thinking and I quickly realized what was creating those httpd processes. I opened up System Preferences (Applications > System Preferences) and navigated to the Sharing pane, identified by a blue folder with a yellow street sign on it.
Inside sharing, I disabled "Web Sharing" by unchecking the checkbox to the left of the option. If the box is grayed out, you'll need to click the lock in the bottom left corner of the window and enter your administrator password.
If you've got "Internet Sharing" enabled you should probably uncheck that, too. But nothing else seemed to be running an httpd daemon. Without either of the net-aware sharing options enabled, TinyUmbrella TSS Server started up without a hitch.
If you've got other apps that create httpd instances (a local web-development environment such as the Acquia Drupal Stack Installer, you'll probably have to shut those down, too).