Over the years I have noticed that my BlackBerry 9700 and then 9800 would sometimes not connect to my Wi-Fi network. This would usually happen when I walked downstairs (Poor Wi-Fi coverage) and then came back up and stood mere feet from then access point. It turns out that there may actually be a reason for this happening and a quick fix if it does.
Mel let me know that RIM has a knowledge base entry that mentions an interesting “Blacklisting” feature that is in BlackBerry OS 5 and 6. What happens is that your Wi-Fi access point may be blacklisted for 5 minutes if you run into “Poor coverage, environmental issues, or access point equipment”. It kind of makes sense since RIM wants the device to ignore a more powerful network if it is having issues and there are other less strong networks that work. To fix it all you need to do is turn off Wi-Fi and turn it back on again or simply wait 5 minutes.