As an experiment, temporarily remove all
.ace from your G table, so it reads like G:OnInitialize, G.db, etc.
Further, I suspect (but can't confirm) that the following line is the root of your issue. Assuming that your posted code is the first Lua file loaded that isn't a localization file or a library, the tables G and V do not exist as far as AceDB is concerned, but F does. It would greatly help if you posted a zip of your addon for downloading and testing.
What are the full names for F, G, and V? What do they represent? Single letters are beyond vague.
Code:
local F, G, V = unpack(select(2, ...))