What steps will reproduce the problem?
1. Logon.

What is the expected output? What do you see instead?
Expected: no problems. Instead: an error occurs.

What version of the product are you using?
r63

Do you have an error log of what happened?
Yata-r63\\TotemSets.lua:66 attempt to get length of field '?' (a nil value)\nYata-r63\\TotemSets.lua:9 in function `InitTotemSets'\nYata-r63\\Core.lua:42 in function <Interface\\AddOns\\Yata\\Core.lua:40\n(tail call): ?:\n<in C code>: ?\n<string>:\"safecall Dispatcher[1]\":9: in function <[string \"safecall Dispatcher[1]\"]:5>\n(tail call): ?:\nAceAddon-3.0-5 (Ace3):531: in function `EnableAddon'\nAceAddon-3.0-5 (Ace3):621: in function <Interface\\AddOns\\Ace3\\AceAddon-3.0\\AceAddon-3.0.lua:607\n<in C code>: in function `LoadAddOn'\nLibPeriodicTable-3.1-90006:170: in function <...le-3.1\\LibPeriodicTable-3.1\\LibPeriodicTable-3.1.lua:167\nLibPeriodicTable-3.1-90006:190: in function <...le-3.1\\LibPeriodicTable-3.1\\LibPeriodicTable-3.1.lua:187\nLibPeriodicTable-3.1-90006:241: in function `GetSetTable'\nMendeleev-3.0\\Mendeleev.lua:188 in function <Interface\\AddOns\\Mendeleev\\Mendeleev.lua:168\n(tail call): ?:\n<in C code>: ?\n<string>:\"safecall Dispatcher[1]\":9: in function <[string \"safecal", -- [1]
                "l Dispatcher[1]\"]:5>\n(tail call): ?:\nAceAddon-3.0-5 (Ace3):531: in function `EnableAddon'\nAceAddon-3.0-5 (Ace3):621: in function <Interface\\AddOns\\Ace3\\AceAddon-3.0\\AceAddon-3.0.lua:607\n\n  ---

Please provide any additional information below.
Upgraded to r63 from r62. First logon of a low level shaman after the 3.1 patch & version upgrade (he has all totems) and the error occurred. A subsequent logon, the error did not happen again.