from bitminter, and bigltc, both will often report my miners as not mining and inactive, although they are running and even generate work. the work is acknowledged by both sites but it lists the number of active workers as 0. why does this happen?
Mining pool servers and websites don't actually know your real hashrate. They try to estimate it based on how often you send in proofs of work (aka "shares"). If your hashrate is very low it won't be possible to make a good short-term estimate and it looks to the website as if you have stopped mining. That's what causes this issue.