I get the same problem with my web and walk internet conection throught my nokia N70 that connects through wireless bluetooth normaly i have to reset the phone and laptop.
For me it happens about 1 hour or 3o min's then the connection and phone crashes out.
I would say for wireless it might be that your using to many connections through one access point if you have more pc's connected to the network.
I would check if the berklin site has a updated driver that could resove the issue.
Or check if there's anythink blocking the signal.
Hope this helps.