Hi Chroma,
This is the same situation I was in with MMTE a few months back.
I had purchased MMTE when it was trading in the .0005 range (a while ago). Was no problem with my Broker (Questrade) to buy AND sell then.
When MMTE hit .0021 about 2 months ago I decided to sell. When I tried to place a sell order through my normal method, it was declined. I called them and they stated things had changed and I needed to use another option to sell them. I asked if I would be charged for doing it this way, and was told no. I was able to sell with the normal commissions.
Then about a month ago, when I tried to buy, I was informed "All trading Halted" for the security. I called them and was told it was on the DTC ineligible list.
So, my broker went from a "Can Buy, can Sell", to a "Can't buy, but can sell", and finally to a "Can't buy, can't sell" scenario.
The only reason i can think of that they allowed me at one point to sell and not buy, is maybe my broker was not being charged the fees from Penson to sell, so they would allow me to sell, or it just took a while for the no sell thing to come into effect.
If you have MMTE through ameritrade right now, I would call them and ensure that in the future you will be always able to sell it. See what they say. I don't really understand all this, but looks like a broker can put a no sell at any time, being that there is now a no buy in effect.