My memory is hazy, because at the time I was in the car mentality of "lol! v-tec sux Ford's 4.6 v8 dix" "Toyota, El Camino, GNX blah blah blah." So, I'm probably not the most reliable source for this. But as I remember it, it was post bailout, either when the government was taking over GM and its assets or when old GM was transitioning into new GM. From what I understand, contracts were being rewritten, loans and debts were being renogotiated, assets were being bought and sold, and people thought it would be a good idea to buy GM stock because it was cheap. The problem was, GM as a company was gonna become a completely different entity, legally speaking, so for some reason GM and the government said GM stocks weren't good for anything, so they told people (multiple times actually) to stop buying GM's stocks. If that's not confusing, the real question I have that maybe you could answer is why they didn't either A) stop selling the stocks altogether or B) make the stocks worth a piece of new GM? Both of those options sound reasonable to me.