Just updated to 0.91 and get, I believe, the same error the first time I open my smelting window:
File: Interface\AddOns\KC_Items\KC_ItemsUtils.lua
Line: 11
Count: 2
Error: bad argument #1 to `strfind' (string expected, got nil)
I get this with my Engineering window:
String: Interface\AddOns\KC_EnhancedTrades\KC_Enhan...
Line: 120
Count: Infinite
Error: attempt to concatenate local `reagentName' (a nil value)
And although I get no error when I open my Beast Training window (I'm a hunter), the window contains no data. When I disable KCET, the data shows up again.