There is a minimum cap on total energy (I believe it is 60) that will prevent you from selling reactors if you would fall below that limit. Considering you are trying to sell it out of your cargo hold, the game's programing is probably keyed to all reactors and not just those that actually break the cap.
As a simple fix for Dan: make it so it calculates the energy drop before it assumes that the reactor can't be sold. (test: if max energy < cap when sold, then reactor sell = false)
_________________I have suggested 7 Races, 5 Organizations, 3 locations, 3 materials, and 20 planets.
View my profile interests for a full list.