I believe this one is either caused by a DDoS(Probably not) or if you have multiple tabs open(Most likely). How many tabs do people have open when this happens?
It doesn't happen to me. And no, it's caused because of too many connections to the site (traffic) but only Noreturn has received it (twice). HF has this error a lot.
Sql connections are to be simple 25 posts at one time. Anymore you get errored but there are also some running to keep the connection open. so you problery dont get 25 u get like 17
It's not the amount of posts that results in connections. It's amount of queries at a time. Opening a page goes through SQL and creates a query. 25 of these (normally a bit more) is creating too many connections error.