The addon still appears to work but this error is generated upon the loading.

4x XanDurability/config.lua:137: attempt to call global 'InterfaceOptions_AddCategory' (a nil value)
[string "@XanDurability/config.lua"]:137: in function <XanDurability/config.lua:92>
[string "@XanDurability/config.lua"]:144: in function EnableConfig' [string "@XanDurability/xanDurability.lua"]:96: in function EnableAddon'
[string "@XanDurability/xanDurability.lua"]:46: in function <XanDurability/xanDurability.lua:35>

Locals:
about = XanDurabilityAboutPanel {
name = "XanDurability"
}
fields =

{
1 = "Version"
2 = "Author"
}
notes = "A small window that displays the total current armour durability."
title = FontString {
}
subtitle = FontString {
}
anchor = FontString {
}
(*temporary) = nil
(*temporary) = XanDurabilityAboutPanel {
name = "XanDurability"
}
(*temporary) = "attempt to call global 'InterfaceOptions_AddCategory' (a nil value)"
ADDON_NAME = "XanDurability"

Apparently the recent patch as well as the changes found in next expansion TWW, is causing a lot of bugs. I'll tackle these one at a time.

This bug seems very similar to one I had with BagSync. I'll need to compare.