May have something to do with Heirloom gear.

44x ...pie/Libs/LibClassicInspector-9/LibClassicInspector.lua:3099: attempt to perform arithmetic on field '?' (a nil value)
[string "@Groupie/Libs/LibClassicInspector-9/LibClassicInspector.lua"]:3099: in function <...pie/Libs/LibClassicInspector/LibClassicInspector.lua:3083>
[string "@Groupie/Libs/LibClassicInspector-9/LibClassicInspector.lua"]:3157: in function <...pie/Libs/LibClassicInspector/LibClassicInspector.lua:3153>

Locals:
s = "01-2000000000000000000000000003050331103050233152312312120500002110100000000000000000030000500020000000000000000000000000000040000000023053513120023103331103123000000100"
(for index) = 2
(for limit) = 2
(for step) = 1
x = 2
(for index) = 4
(for limit) = 6
(for step) = 1
i = 4
z = 405004
(temporary) = "01-2000000000000000000000000003050331103050233152312312120500002110100000000000000000030000500020000000000000000000000000000040000000023053513120023103331103123000000100"
(temporary) = defined =[C]:-1
(temporary) = nil
(temporary) = 405004
(temporary) = 237641
(temporary) = 1
(temporary) = 405004
(temporary) = 237641
(temporary) = 9
(temporary) = 3
(temporary) = 3
(temporary) = 3
(*temporary) = "attempt to perform arithmetic on field '?' (a nil value)"
isWotlk = true
glyph_r_tbl =

{
63219 = 23
63223 = 26
63225 = 28
57937 = 1
54923 = 2
54925 = 4
54927 = 6
54929 = 8
54931 = 10
54935 = 12
54937 = 14
54939 = 16
54943 = 18
57979 = 6
63218 = 22
63220 = 24
63222 = 25
63224 = 27
54922 = 1
54924 = 3
54926 = 5
54928 = 7
54930 = 9
54934 = 11
54936 = 13
54938 = 15
54940 = 17
57958 = 5
57955 = 4
57954 = 3
57947 = 2
56416 = 20
56420 = 21
56414 = 19
}
SendAddonMessage = defined =[C]:-1
C_PREFIX = "LCIV1"

I don't think it's related to heirlooms. That line was about glyph data.
You might have been on a class who's glyphs got changed in P2.
If the library update doesn't fix it (I logged in with a toon wearing heirlooms and got no error) this can be re-opened.

If the error happens again (at a line close to the previously reported) post the glyph configuration of the toon getting the error.

@Road-block

This happens when you log in with a toon wearing heirlooms.