Can`t see the EX4100 with WD Access, unit freeze, and I have to restart it unpluging the power cord

I have a WDEX4100, I have experiencing in two time the next behavior; After a week end, At start the activity, I can’t connect with the NAS using the WD Access (Mac computer), I can’t see the Name of the disk menu to open the disk to work, the only menu that are available are the about and quit menu, to be able to have access again to the NAS unit, I have to shut down it, but the unit is freezed, I can`t shut down it using the button in it, I have to disconect the power cord and I recconect it, then I can see the unit an access to it.

How can I shut down propperly the unit when it`s freeze wiht out have to unplug the power cord?, and does anyone have the same behavior? does anyone knows wich is the reason of it?

I have turned on the auto up date firmaware feature, a power schedule for week end and a scan for virus schedule all modays at 6:00 am, can some of this freeze the NAS sistem?

Any help wold be helpfull.