I have the same problem with a LS-W4.0TL/R1 Storage.
Randomly, it lost connection to the network. I can't acess through any method, like Nas Navigator, web interface or windows. I know that aren't any problems in the network because I can see the storage on the LAN client list of my router. To get worse, the storage doesn't respond when I try to shut down. It remains only with the blue LED light not blinking, as if was everything okay.
I've just upgraded its firmware today to the lastest version (1.41) and the problem continues. Usually in 30 minutes it lost conection with the network. The only way to restore the connection is pulling the power cable and powering on again.
edit: the reset method with function button doesn't work too.