8x PallyPower/PallyPower.lua:1518: Usage: ChatThrottleLib:SendAddonMessage("{BULK|
ORMAL||ALERT}", "prefix", "text", "chattype"[, "target"])
[string "=[C]"]: in function error' [string "@AtlasLootClassic/Libs/AceComm-3.0-12/ChatThrottleLib.lua"]:462: in function SendAddonMessage'
[string "@PallyPower/PallyPower.lua"]:1518: in function SendMessage' [string "@PallyPower/PallyPower.lua"]:1411: in function SendSelf'
[string "@PallyPower/PallyPower.lua"]:1533: in function <PallyPower/PallyPower.lua:1525>
[string "=[C]"]: ?
[string "@PallyPower/Libs/AceBucket-3.0-4/AceBucket-3.0.lua"]:69: in function <...dOns/PallyPower/Libs/AceBucket-3.0/AceBucket-3.0.lua:67>
[string "@PallyPower/Libs/AceBucket-3.0-4/AceBucket-3.0.lua"]:83: in function `func'
[string "@Details/Libs/AceTimer-3.0-17/AceTimer-3.0.lua"]:57: in function <...ceDetails/Libs/AceTimer-3.0/AceTimer-3.0.lua:50>

Locals:
(*temporary) = "Usage: ChatThrottleLib:SendAddonMessage("{BULK|
ORMAL||ALERT}", "prefix", "text", "chattype"[, "target"])"

Looks like an issue caused by a different addon with an outdated/incompatible library ( Atlas Loot Classic /Libs/AceComm-3.0-12/ChatThrottleLib.lua). Or maybe not, try to reproduce it with Atlas Loot disabled or update it to latest version.

Libraries like Ace use LibStub to automatically force a single, most up-to-date version to be loaded, even if one addon has an out of date version. So there's nothing wrong with AtlasLoot's version of AceComm; if it was out of date, LibStub would automatically load a newer one from PallyPower. Since they're the same version, it just loads the version from the first addon to include it, alphabetically.

The error seems to be that type is sometimes left nil, likely when a player is in an Instance group but not in an Instance:

likely when a player is in an Instance group but not in an Instance:

Yep, that happened, I released and then the lua error popped-up.

so replacing

elseif IsInGroup(LE_PARTY_CATEGORY_HOME) then

with just "else" should fix it?