i clicked on the icon for first aid and had that window open.. i then clicked on the game icon for cooking and got the following

5x Skillet-Classic\SkilletData.lua:605: attempt to index field '?' (a nil value)
[string "@Skillet-Classic\SkilletData.lua"]:605: in function GetSkill' [string "@Skillet-Classic\SkilletData.lua"]:678: in function CalculateCraftableCounts'
[string "@Skillet-Classic\SkilletQueue.lua"]:32: in function AdjustInventory' [string "@Skillet-Classic\Skillet-20502.nil.lua"]:846: in function ?'
[string "@datastore\libs\CallbackHandler-1.0\CallbackHandler-1.0-7.lua"]:119: in function <...ore\libs\CallbackHandler-1.0\CallbackHandler-1.0.lua:119>
[string "=[C]"]: ?
[string "@datastore\libs\CallbackHandler-1.0\CallbackHandler-1.0-7.lua"]:29: in function <...ore\libs\CallbackHandler-1.0\CallbackHandler-1.0.lua:25>
[string "@datastore\libs\CallbackHandler-1.0\CallbackHandler-1.0-7.lua"]:64: in function `Fire'
[string "@datastore\libs\AceEvent-3.0\AceEvent-3.0-4.lua"]:120: in function <DataStore\libs\AceEvent-3.0\AceEvent-3.0.lua:119>

closing the first aid window then opening the cooking window gave no error at that point then i was able to keep the windows open and switch between first aid and cooking..

hope that helps narrow it down

This particular error should be eliminated in Skillet-Classic-1.35-alpha1 and beyond. Please reopen this issue or open a new one if it happens again.

I'm going to guess that this happened the first time you were opening cooking after logging in. If so, then this is another manifestation of issues #40 and #45. The Blizzard API that Skillet-Classic uses queries the client but the data originates on the server. The API returns what the client knows at that time even if it is incomplete and/or wrong. Unfortunately, there's no event available to indicate that the client has all the data.

I have attempted to code Skillet-Classic to mimic the Blizzard UI and have obviously failed. I have asked for additional information in #40 and #45 but neither has responded. Until I can collect enough debug information to discover a pattern and develop a fix, this issue will remain unsolved.

Opening and closing each profession once at the beginning of each session appears to prevent these errors.