WoW-Pro-Guides release v2.1.4 as well as latest alpha build b133399, WoW 4.0.6.13623 live, USEnglish client/server. Logging on with either of those two mod builds active, the following error comes up in FrameXML.log:

3/1 01:45:08.603 ** Loading table of contents Interface\AddOns\WoWPro_Leveling\WoWPro_Leveling.toc
3/1 01:45:08.603 ++ Loading file Interface\AddOns\WoWPro_Leveling\Alliance\Guides.xml
3/1 01:45:08.603 Error loading Interface\AddOns\WoWPro_Leveling\Alliance\70a_70a_Crackerhead22_Shadowmoon.lua
3/1 01:45:08.603 Error loading Interface\AddOns\WoWPro_Leveling\Alliance\70s_70s_Crackerhead22_Shadowmoon.lua

This is due to the fact that with \AddOns\WoWPro_Leveling\Alliance\Guides.xml in those two mod versions, pointers are given to those two files, but they don't actually exist. Instead, they have been replaced by the following file which is not mentioned in Guides.xml: 70_70_Crackerhead22_Shadowmoon.lua.

So \Alliance\Guides.xml needs updating, especially since the problem is present in the 2.1.4 release version.

Fixed in df5c42d .

BTW: Thanks for mentioning FrameXML.log!
Now I will add it to my checklist for releases so this does not happen again.