Here's an odd one. My Android tablet frequently says that my home wifi "is known to Android but signal is too weak/too far away to connect" even when it's a few feet from the router.
At the same time the tablet happily locks onto wifi from the local town 3 miles and 600 feet lower.
The cure for the tablet is turning wifi off and on again when my home wifi pops up nice and strong on the screen. Needless to say no problems connecting to free wifi everywhere else. And my HTC phone has no problems conecting to my home wifi: it's just the tablet.
Any clues ?