@Jotin
I do not believe this is something specific to the PC. I have 3 systems connected to the NAS: A laptop, two desktops (the two desktops have different mainboards, obviously also different hard drives). What is common to all of them: OS Win 7 prof., AVG 2011 Antivirus, all other network security settings are the same. The symptoms are all the same for all PCs: The NASNavi will wake-up the NAS, (b.t.w. with 1.40 firmware the time to boot the NAS is long, several minutes !, this was better with former firmeware, looks like an other issue). Typically, then after the NAS is booted I can see and access the share folders. But then after a while, can be several 10s of minutes or some hours, the connection and access is all sudden gone, typically during access when writing data to the NAS (otherwise I would probably not notice). And, it does not really matter what the ntml settings are, consistent with what others write. So I do not buy the story with ntml settings, seems to be not relevant at all. The bad thing is, the last time this happened, during access and writing, after re-booting the NAS Webadmin says (Volume not formated ). It still sees the NAS, sees the RAID 0 volume, however, lost the format information. This has nothing to do with the OS, antivirus, or firewall. Reading through the forum it seems to be not un-common that hard drive or RAID information is lost for this prduct. In any case, nothing is wrong with the format, I checked with UFC Explorer Professional, the RAID 0 can be rebuild and data can be accessed without any problem or re-formating. Thus it is definitely the NAS that lost the drives and RAID, maybe caused by the fact that access was interrupted suddenly (I could imagine that).
Was I re-build it I will check your suggestion with security essentials, but I doubt it. Why should antivirus cause it and why should microsoft security essentials be better in that ?
I noticed one thing however during NASNavi installation: I had it that right after NASNavi software installation once Win build in firewall pop-up telling that it blocked NasNavi. I found this weird, allowed access and checked the firwall setting: NASNavi has accesss to home and public network, the blocking did not show up again, but maybe there is something related to that I do not realize. Any clue why the firwall could have poped-up during/short after NASNavi install ?