question on low hands, please!

[bodie]

Last night I ran into a situation I realize I don't exactly understand (and lost money on it as well!).

If final board reads:

2 3 4 5 Q (all unsuited)

and my hand is:

A 6 Q K

With four cards on the board that are low, isn't my Ace a "live" Ace?
Another hand won the low with:

A 2 X X

I don't understand why his 2 wasn't counterfeited -? If it's because there were four lows on the board, then why didn't my hand also win the low? Is it because my 6 was too much of a stretch to fit into the straight with my Ace? (With the "four low card" situation, I don't quite understand.
Is that also why the 6 that I had would not count as a low if all the other lows were already on the board? Because of the four low card rule?

Help!