it would be nice to know what causes the error condition
Indeed it would but.....
The most rock-solid connection to my wifi router is the HTC phone (when it doesn't latch on to the ten or twelve other wifi systems in the neighbourhood that I haven't clicked as "ignore" that is). The worst at connecting is the Acer Aspire One.
But there are times when connection is impossible and I have to reset the router. Comes back on, same parameters as before, but this time all devices (which I've left running and looking for it) happily latch on to it.
Most knowledgable people I've talked to say "from time to time it just happens".