Also remember that once someone downloads an official ROM from Samsung's server, it gets added in SamMobile Firmware Directory so try to find it there first.
I kept getting the same error as webup regardless of deleting the file when using the gui client. So tried the command line and again no luck. This is what I got -
The screenshot shows that the error is with downloading the file, everything else seems to be fine, this could be an Anti-virus/firewall issue, might be your DTSL model configuration, or could be a permission problem.
Try disabling the antivirus/firewall, if this doesn't work, try another computer, maybe another network (work or friend's computer) and remember to run the command line as an administrator.
Can this stock rom be flashed by CWM ????? or do you have to use Odin? I have the stock rom downloaded through Checkfus and when I tried install from internal SD (in CWM) it gave an error of cannot open the file GT-I9300_NZC_1_20120514193747_pm44bqucec.zip