Not much to go on here but I'll give it a shot. What phone/device? What did you remove and how did you remove it?

android.process.acor is the People (AKA, "Contacts") app. Many seemingly unrelated apps are co-dependent, and removing one can cause problems in another. For example, if you had Facebook contact sync enabled and then simply deleted Facebook without first removing sync and logging out of Facebook, it would cause acor errors.

 

Excuse me if I'm over-simplifying, but I don't know your background experience. Realize that system apps don't get "installed" in the normal sense. The .apk (and .odex, if there is one) get moved to /system/app or /system/priv-app. Next, the file permissions have to get set to 644. It's also a good idea to delete the dalvik cache (i.e., the contents of /data/dalvik-cache). Finally, reboot.

The first thing you'll see after the boot animation is a "Android is upgrading" message. This is the result of it seeing the new system app and building the Dalvik cache for it. If you deleted the cache entirely, it will take longer of course, since it has to rebuild potentially hundreds of file cache entries. It's all perfectly normal; just be patient. Assuming you don't have any missing .odex, library files, or symlinks needed for the program to run, everything should be good to go once the phone boots fully. Problems occur when you partially delete stuff or don't know what was deleted. I have backups of most of the AT&T bloatware from my old S4 (on Android 4.3), so if you can tell me specifically what you need or what is not working, I might be able to provide you the missing files. Failing that, your only solution is to start over by flashing a factory ROM (a factory data reset won't help).

Here are the app packages I have available (sorry, MMS isn't one of them):

 

It's easier to just load TWRP Manager, which gives you the option to install TWRP directly. Once installed, you'll also be able to use the manager app to administer TWRP functions without having to boot to recovery first.

If you need to install via computer for some reason, instructions are on the TeamWin page for adb, but not odin: http://teamw.in/project/twrp2/174

There are instructions here for odin, but it's for the i9505 variant of the S4, so use at your own risk.

 

I guess that leaves the recovery image method. Follow the instructions in the second link of my previous post. It is specifically for your model phone. Pay attention to the warning about getting the number correct in the adb/emulator command (in "mmcblk0p21" the fourth character from the end is a ZERO, not an upper-case-o).

 

That was going to be my final suggestion. The steps on the site you linked to look sound, but I never heard of it before. I would suggest one modification to those instructions, and download the firmware from Sammobile instead. GL!