OSX Maveric and RN 516 - smb problem #25261052

Yesterday I suddenly had trouble accessing from 2 mac. Now every day something happens absurd. User "administration" that has access to all folders and graphics to a folder "Administration" (containing the accounts). We tried to restart the Mac, but to no avail. The absurd thing is that one of the mac could connect I could read but not write. I tried several times to copy files, seemed to me an error message of course, in some cases, the files were copied in other cases, however, entirely copied but with Zero Kb. This morning it worked a bit ', then again the same problem . Then without rebooting anything I changed the password to the user administration and reset the permissions to the folder accounting and reconfigured accesses identical to the first. Now it works, but I do not know how long it will go on. Today will not let me save you from illustrator and photoshop, but the folder has read and write permissions. I have to re-configure the permissions to the shared folder so it works again. I throw this NAS. Never seen anything like in 30 years of my graphic design agency. If I take a stupid USB drive and share it on the network PC and Mac it works as a marvel. Or I restart my old xserve. I spent 1,500 Euros to double check the entire network (a new network), I changed the HUB and trashed the old still working. At this point what could be? Perhaps for netgear will be due to the Mac or PC, but at this point what I can work with?
Windows XP Windows 8 no !, No! OSX 10.4 no! OSX Snow Leopard no! Yosemite No? I try to install linux on all machines? Netgear thanks!!!