[AT&T Samsung Galaxy S 4 Q&A, Help & Troubleshootin] spocko:
Gave up on original Win 7 x64 computer. Switched to another computer with Win Vista x32. As be.fore, this computer has never had phone drivers or Kies installed. When I plug the phone into the computer, Windows successfully detects it and I can browse the files in Windows Explorer. And yes the phone definitely has USB debugging mode enabled.

With the last couple of nightly builds, CASUAL tells me that the phone is detected. However, there seems to be an error in those builds because the script is missing. Looking in the temp folder where CASUAL extracts the files, there is no SCRIPTS subfolder. Therefore the "Do It" button does nothing. Here is an example log:

[DEBUG]working
[INFO]We are running Windows Vista
Creating Temp Folder in:C:\Users\Admin\AppData\Local\Temp\CASUALAdmin-2013-07-31-22.49.17\CASUAL Cross-platform Android Scripting and Unified Auxiliary Loader
Revision:778 build:6,497
CASUAL Copyright (C) 2013 Adam Outler
This program comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to redistribute it, under certain conditions; run
'C:\Users\Admin\Downloads\gs4\Root-and-Recovery-ATT-TMO-GS4-CASUAL-R778b--Nightly.jar --license'
for details. http://android-casual.googlecode.com for source.
[DEBUG]launching GUI
[DEBUG]Picking Jar File:/C:/Users/Admin/Downloads/gs4/Root-and-Recovery-ATT-TMO-GS4-CASUAL-R778b--Nightly.jar ..scanning.
[DEBUG]Found Windows Computer
[DEBUG]Attempting to write C:\Users\Admin\AppData\Local\Temp\CASUALAdmin-2013-07-31-22.49.17\Elevate.exe
[DEBUG]File verified.
[DEBUG]Attempting to write C:\Users\Admin\AppData\Local\Temp\CASUALAdmin-2013-07-31-22.49.17\adb.exe
[DEBUG]File verified.
[DEBUG]Attempting to write C:\Users\Admin\AppData\Local\Temp\CASUALAdmin-2013-07-31-22.49.17\AdbWinApi.dll
[DEBUG]File verified.
[DEBUG]Attempting to write C:\Users\Admin\AppData\Local\Temp\CASUALAdmin-2013-07-31-22.49.17\AdbWinUsbApi.dll
[DEBUG]File verified.
[DEBUG]Searching for scripts
[DEBUG]Setting executable C:\Users\Admin\AppData\Local\Temp\CASUALAdmin-2013-07-31-22.49.17\adb.exe. Result=true
[VERBOSE]ADB Server Started!!!
[VERBOSE]TimeOut on C:\Users\Admin\AppData\Local\Temp\CASUALAdmin-2013-07-31-22.49.17\adb.exe after 5000ms. Returning what was received.
[DEBUG]Controls Enabled status: true
[DEBUG]State Change Detected, The new state is: 1
[DEBUG]Device Connected
[DEBUG]@stateConnected
[DEBUG]Controls Enabled status: true

Going back to the last instabuild R773b, it does properly extract the SCRIPTS folder, but it never detects the phone (or detects it only momentarily). Here's the log:

[DEBUG]working
[INFO]We are running Windows Vista
Creating Temp Folder in:C:\Users\Admin\AppData\Local\Temp\CASUALAdmin-2013-07-31-22.56.50\CASUAL Cross-platform Android Scripting and Unified Auxiliary Loader
Revision:773 build:6,423
CASUAL Copyright (C) 2013 Adam Outler
This program comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to redistribute it, under certain conditions; run
'C:\Users\Admin\Downloads\gs4\Root-and-Recovery-ATT-TMO-GS4-CASUAL-R773b--InstaBuild.jar --license'
for details. http://android-casual.googlecode.com for source.
[DEBUG]ClassJar:jar:file:/C:/Users/Admin/Downloads/gs4/Root-and-Recovery-ATT-TMO-GS4-CASUAL-R773b--InstaBuild.jar!/CASUAL/CASUALTools.class
[DEBUG]launching GUI
[DEBUG]Picking Jar File:/C:/Users/Admin/Downloads/gs4/Root-and-Recovery-ATT-TMO-GS4-CASUAL-R773b--InstaBuild.jar ..scanning.
[DEBUG]parsing SCRIPTS/
[DEBUG]Found Windows Computer
[DEBUG]Attempting to write C:\Users\Admin\AppData\Local\Temp\CASUALAdmin-2013-07-31-22.56.50\Elevate.exe
[DEBUG]File verified.
[DEBUG]Attempting to write C:\Users\Admin\AppData\Local\Temp\CASUALAdmin-2013-07-31-22.56.50\adb.exe
[DEBUG]File verified.
[DEBUG]Attempting to write C:\Users\Admin\AppData\Local\Temp\CASUALAdmin-2013-07-31-22.56.50\AdbWinApi.dll
[DEBUG]File verified.
[DEBUG]Attempting to write C:\Users\Admin\AppData\Local\Temp\CASUALAdmin-2013-07-31-22.56.50\AdbWinUsbApi.dll
[DEBUG]File verified.
[DEBUG]parsing SCRIPTS/-build.properties
[DEBUG]parsing SCRIPTS/GS4 Root and Loki Recovery.meta
[DEBUG]parsing SCRIPTS/GS4 Root and Loki Recovery.scr
[DEBUG]parsing SCRIPTS/GS4 Root and Loki Recovery.txt
[DEBUG]parsing SCRIPTS/GS4 Root and Loki Recovery.zip
[VERBOSE]found zip at SCRIPTS/GS4 Root and Loki Recovery.zip
[DEBUG]parsing SCRIPTS/-logo.png
[DEBUG]parsing SCRIPTS/-Overview.txt
[DEBUG]

Starting CASPAC unzip.
[DEBUG][TRANSLATION]@noUpdateRequired
[INFO]Verified up-to-date.
[DEBUG]unzip of SCRIPTS/GS4 Root and Loki Recovery.zip is beginning.
[VERBOSE]Unzipping busybox
[VERBOSE]Unzipping pwn
[VERBOSE]Unzipping Superuser.apk
[VERBOSE]Unzipping su
[VERBOSE]Unzipping recovery.img
[VERBOSE]Unzip Complete
[DEBUG]unzip of SCRIPTS/GS4 Root and Loki Recovery is complete.
[DEBUG]Searching for scripts
[INFO]misc hacks for AT&T Galaxy S4

[DEBUG]adding SCRIPTS/GS4 Root and Loki Recovery to UI
[INFO]
[DEBUG]Setting executable C:\Users\Admin\AppData\Local\Temp\CASUALAdmin-2013-07-31-22.56.50\adb.exe. Result=true
[VERBOSE]ADB Server Started!!!
[VERBOSE]TimeOut on C:\Users\Admin\AppData\Local\Temp\CASUALAdmin-2013-07-31-22.56.50\adb.exe after 5000ms. Returning what was received.
[DEBUG]Controls Enabled status: true
[DEBUG]State Change Detected, The new state is: 1
[DEBUG]Device Connected
[DEBUG]@stateConnected
[DEBUG]Controls Enabled status: true
[DEBUG]State Change Detected, The new state is: 0
[DEBUG]@stateDisconnected
[DEBUG]Device Removed
[DEBUG]Controls status: false

The originally posted build 527 also does not detect the phone. Here's a log from that version:

[INFO]We are running Windows Vista
Creating Temp Folder in:C:\Users\Admin\AppData\Local\Temp\AdminTEMPCASUAL9F5DDC95\CASUAL Cross-platform Android Scripting and Unified Auxiliary Loader
Revision:527 build:3,811
CASUAL Copyright (C) 2013 Adam Outler
This program comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to redistribute it, under certain conditions; run
'C:\Users\Admin\Downloads\gs4\Root%20and%20Recovery%20for%20ATT-TMO%20GS4-CASUAL-R527b.jar --license'
for details. http://android-casual.googlecode.com for source.
[DEBUG]Picking Jar File:/C:/Users/Admin/Downloads/gs4/Root%20and%20Recovery%20for%20ATT-TMO%20GS4-CASUAL-R527b.jar
[DEBUG]Found Windows Computer
[DEBUG]Found: GS4 Root and Loki Recovery
[DEBUG]OMFGWOOT GUI running!
[INFO]misc hacks for AT&T Galaxy S4

[DEBUG]Searching for scripts
[DEBUG]Updating Scripts for UI
[VERBOSE]From Resource: true
[INFO]--GS4 Root and Loki Recovery--
[INFO]This will install root and recovery for you Qualcomm based Samsung Galaxy S4

##############################
# Motochopper Copyright (C) 2013 Dan Rosenberg (@djrbliss)
# Loki Copyright (C) 2013 Dan Rosenberg (@djrbliss)
# TWRP recovery - Team Win
##############################
# Instructions:
# 1. Put your device in debugging mode
# 2. Attach it via USB
# 3. Click the Do It button
##############################

[DEBUG]Created zipResource at /SCRIPTS/GS4 Root and Loki Recovery.zip
[DEBUG]Exiting comboBoxUpdate()
[DEBUG]attempted to lock controls but controls are not availble yet
[DEBUG]Extracting archive....
[DEBUG]Target Script Is resource
[VERBOSE]Unzipping busybox
[VERBOSE]Unzipping pwn
[DEBUG]Attempting to write C:\Users\Admin\AppData\Local\Temp\AdminTEMPCASUAL9F5DDC95\Elevate.exe
[DEBUG]File verified.
[DEBUG]Attempting to write C:\Users\Admin\AppData\Local\Temp\AdminTEMPCASUAL9F5DDC95\adb.exe
[VERBOSE]Unzipping Superuser.apk
[DEBUG]File verified.
[DEBUG]Attempting to write C:\Users\Admin\AppData\Local\Temp\AdminTEMPCASUAL9F5DDC95\AdbWinApi.dll
[VERBOSE]Unzipping su
[VERBOSE]Unzipping recovery.img
[DEBUG]File verified.
[DEBUG]Attempting to write C:\Users\Admin\AppData\Local\Temp\AdminTEMPCASUAL9F5DDC95\AdbWinUsbApi.dll
[DEBUG]File verified.
[DEBUG]sleeping for Windows ADB start
[VERBOSE]Unzip Complete
[DEBUG]Attempting to write C:\Users\Admin\AppData\Local\Temp\AdminTEMPCASUAL9F5DDC95\adb_usb.ini
[DEBUG]File verified.
[DEBUG]###executing: C:\Users\Admin\AppData\Local\Temp\AdminTEMPCASUAL9F5DDC95\adb.exe###
[VERBOSE]List of devices attached
[DEBUG]Device List:

[DEBUG]unknown

At this point I've wasted several hours trying to get this tool to work and have gotten nowhere, so I'm feeling pretty frustrated. :(