I got my HTC Inspire 4G about three weeks ago. I connected it to one router and it worked fine. Then I attempted to connect it to another router, but it didn't work until I downloaded an app called Wifi Manager and inputted my network information manually. This networked worked very briefly before it stopped. Afterwards, all other networks I connected my phone to ceased to work, even after uninstalling the app.
In all cases, it actually connects to the router, but webpages won't load and the Market gives me a network error.