Ubuntu Networking :: Wireless "connection Established" No Browse No Ping

Ubuntu 11.04, wireless adapter BCM4312.The connection works for a while, for a random length of time from a few minutes to a few hours, then stops working. The laptop says it's connected, and the router says it's connected, but the browser can't find any Web pages, it can't find the router, and there is no response to pings from the router or any other device on the local network or on the Internet. "Host unreachable." When I try to ping to the laptop from another one, it times out.If I shut down the computer and try again a few hours later, it works fine again for a while, then after a while it stops working again.

In case it's relevant, sometimes when I restart networking from the command line, it says "ignoring unknown interface eth1=eth1," even though ifconfig -a lists eth1 as up with an ip address. eth1 is the wireless adapter. Another laptop with Ubuntu 11.04 connects to the same router with no problems.Using a fixed IP address doesn't change anything.