I am having a similar issue and would appreciate some advice.  For a while, Windows 7 worked just fine with the DNS-321.  Lately, however, even when mapping using easy search, transfers fail after about 8gb.   I am transferring large files (30 gb) of Bluray material that I have want to transfer from my discs to the DNS321 for archival purposes.  
I seems like the DNS321 is somehow not responding to network requests.  Any ideas on how to keep it "alive"?