Just because the TV can play a WMV file, does not mean it can play all WMV files, as WMV files vary with resolution, bitrate, etc depending on the video itself. If it plays fine via usb then yes, you likely have a network issue.
The file is too big to copy to a USB drive because FAT32 file format has limits. Re-format to NTFS and you should be able to copy it, but I don't know if the TV can read an NTFS thumb drive, some are limited to FAT and FAT32 formats. In that case, I don't know what you can do to test locally except find a way to split the file into smaller pieces (video editing software).
Playing on a laptop via HDMI won't necessarily tell you anything, unfortunately. If you can play it on the laptop itself, it will play via HDMI just the same. I assume it is a windows laptop, windows is much more forgiving when it comes to wireless network quality issues than your Samsung TV.
While its most likely your wireless connection, IMO, one other thing that you might check is if you NAS is transcoding, which is essentially re-encoding the file as it is streamed to the TV. Some NAS DLNA software will do this by default, you could try looking at any settings on your NAS and turn transcoding on/off if indeed that is a feature it has.