"...ask is for 999 lots at $0.79. A trade is made at $0.79 for 2000 shares, and there is still 999 lots on offer..."
Just guessing here, but I suspect that, at least on TDW's WebBroker, the 999 means that there are 1000 or more lots. I don't think I've ever seen lot numbers larger than 999.
I just took a look at Breakwater Resources, and it shows 999 lots at bid, and 999 lots at ask. That would be too much of a coincidence, so I would assume that 999 is the maximum that TDW displays.