Okay, let's try:
In Sources/AdvancedTabs.pm find

## End Mod hook tablist ## 

Add above it

    push @tablist, 'quiz'; 

Check in Settings.pm:  the @AdvancedTabs list should have 'quiz' in it somewhere. If not this needs to be added to the bottom of Settings.pm, just above the 1;

push @AdvancedTabs, 'quiz'; 

Corrected Quiz.pm in new zip.

ARGH!! 

In Quiz.pm find

    require Sources::Postbox; 

and change it to

    require Sources::PostBox; 

I'm guessing it didn't throw the error on my test server because that server is on Windows, which is case insensitive for file names.

I'll have a new zip in the morning.

No - I actually found it, finally. There were insufficient tests for a file that ManageQuiz.pm or Quiz.pm were supposed to create - it was being required before it was created. 

What frustrated me was I would get the error once, and not be able to repeat it. 

New zip in 1st post. (Quiz.pm needs to be replaced, too.)

This is absolutely frustrating.

Quiz Mod for YaBB 2.6.11
Version: 0.7.7

This mod allows you to setup a quiz center on your boards quickly and easily.
This quiz center has an advanced Admin script for managing the quiz displays.
All users can enter own quizzes. The admin can restrict this so that only admins can add new quizzes.
The quiz tracks all results and displays high scores.
Upon completion, users are given a total quiz breakdown of the quiz, showing them how they fared on each question, and, on the ones they missed, showing them the correct answer. Upon completion, users are shown a graphical bar representing their score, and a graphical bar representing the average score for the quiz.
A member can take a quiz only once. Main quiz page calculates displays the easiest and most difficult quizzes automatically.
Moreover you can sort quizzes by different items.
This mod supports YaBB Code and the Censor list.

Installation:

- Download your Variables/Settings.pm from your forum
- Apply Quiz mod
- upload modded files

AdminIndex.pl
Admin/Admin.pm
Admin/AdminSubList.pm
Admin/ModList.pm
Languages/English/Admin.lng
Languages/English/Error.lng
Sources/AdvancedTabs.pm
Sources/Load.pm
Sources/PostBox.pm
Sources/Profile.pm
Sources/SubList.pm
Sources/Subs.pm
Sources/TabMenu.pm
Templates/default/Menu.def
Variables/Settings.pm

- upload ManageQuiz.pm to /Admin/Mods directory in ASCII
- upload Quiz.pm to /Sources/Mods directory in ASCII
- upload quiz.lng to /Languages/English/Mods directory in ASCII
- upload quiz.gif to yabbfiles/ModImages
- upload chekgreen.gif, chekyellow.gif, and QuizBar.gif to yabbfiles/ModImages/quiz
- set quiz options in Admin

Note that a user cannot take their own quizzes.
Note: once a quiz has been created or Settings.pm has been saved, Quiz cannot be removed using BoardMod without removing Variables/Settings.pm section from THIS file and hand editing Variables/Settings.pm to remove 'quiz' from the @AdvancedTabs list.

Mod updated by whisper68, bugfixes and compatible with 1.3, 1.3.1
===========
Bug fixes since version .95
Fixed problem with cheat protection (by Carsten, big thx)
Menu item "Quizzes" text class fixed (by whisper68)
Missing folder tree fixed (by Jake, thx)
Register link fixed (by Jake, more thx)
Mod updated by Carsten, bugfixes and compatible with YaBB 2.1
===========
Mod adjustments to fit with YaBB 2.3, no feature adjustments (Batchman) beta 0.1
Small layout fix and added Jet Li's German and German_Du language files beta 0.2
Update for 2.3.1, (beta 0.5) including Carsten's Auto Tabs feature to automate tab creation. This version works for both 2.3 and 2.3.1.

Thanks to Jet Li for info on adding menu tabs.

04/21/09 Updated for 2.4.

10/14-18/10 Updated to 2.5, and a few minor corrections and settings additions. (Thanks, Carsten.)
Updated for 2.6.0 by Dandello
Updated for 2.6.1 by Dandello - Sept 05, 2014
Updated for 2.6.11 by Dandello - Jan 05, 2015
minor tweaks - Jan 21, 2015

Author: Batchman (orig by Phyrron, development by  Whisper68, Carsten, others)
Edited: