with second tftp server I mean, do you have another tftp server active on your windows 8 pc then the one used by fvdw-sl console. In that case the nas connects to the wrong tftp server.
Another explanation can be that the tftp folder is empty but in that case you would not be able to select it or the permission settings for the file are not ok.
Check that they are read/write accessible for the everybody
further this part of your post I do not fully understand
when it asks select directory for the UIMAGE-395-NWSP2CL-179-standalone
It should not ask for a directory but a popup window should appear to select the file
Seems you have changed the default folder setting for tftp directory, do not do that, leave the default value
For the rest I see no other causes :dontknow