Slow data transfer in Windows

I have just purchased a ReadyNAS 2120 v2.  I networked it to my server and copied off an large amount of data (2TB).  The Write time was great.  I then moved the NAS onto my live network.  I uploaded a few more files (5GB) which took about 2 and a half minutes.  I started getting some complaints about slow copying of file down from the NAS.  I went to download one of the .iso files I had uploaded and I was getting transfer speeds of 512/KB and it would drop to ~200/Kb.  I started thinking this might be a Windows Security problem since this was a .iso file.  I moved from the windows machine to a Linux machine and the file tranfer speed down was 30MB which is about what I expected.  I then tried an Apple machine and got the same results about 30MB.  I returned to the Windows machine and attempted to download a different type file (.mkv).  This is also slow 300/kb.  I then repeated everything on Linux and Apple and the transfers were fine.  I downloaded the NAS performance tester and ran it from the Windows machine and it still has not completed the test. (1 hour) later.  The write speed was an average of 13MB. I have verified the jumbo frame setting is off.  I have added the Nas by ip adress and name to the Internet security settings.  I have tried just about everything I have come across with no results.  I have eliminated switch, netcard by using multiple machines.  Do you have any other setting in Windows that might be causing this issue?