I expect you have the latest firmware!? And your machines are in good range or close proximity to the 601.
With wireless networking there are two issues at work here. The first is signal strength and compatibility with your wireless router, the second is your wireless receiver. You should be able to check the signal strength of the wireless router from the network display in the bottom corner. If you are getting good signal strength that is intermittent you might try updating (or even downgrading) the firmware for the wireless router or your system firmware for your wireless receiver card. The second thing you should check is if the router is using an N, N+, G, or some other signal type. The newer model routers are reverse compatible, but you are going to get the best signal strength most of the time if you are using a good name brand router with compatible receiver types, since some of the G routers broadcast in N, N+, or G bandwidth, but the older types do not have the same signal strength or range.