title: Downloading NetCDF files with R: Manually works, download.file produces error
body: <p>I am trying to download a set of NetCDF files from: <a href="ftp://ftpprd.ncep.noaa.gov/pub/data/nccf/com/nwm/prod/nwm.20180425/medium_range/" rel="nofollow noreferrer">ftp://ftpprd.ncep.noaa.gov/pub/data/nccf/com/nwm/prod/nwm.20180425/medium_range/</a></p>
  
  <p>When I manually download the files I have no issues connecting, but when I use download.file and attempt to connect I get the following error:
  Assertion failed!</p>
  
  <p>Program: C:\Program Files\Rstudio\bin\rsession.exe
  File: nc4file.c, Line 2771</p>
  
  <p>Expression: 0</p>
  
  <p>This application has requested the Runtime to terminate it in an unusual way.
  Please contact the application's support team for more information.</p>
  
  <p>I have attempted to run the code in R without R studio and got the same result.</p>
  
  <p>My abbreviated code is as followed:</p>
  
  <pre><code>library("ncdf4")
  library("ncdf4.helpers")
  download.file("ftp://ftpprd.ncep.noaa.gov/pub/data/nccf/com/nwm/prod/nwm.20180425/medium_range/nwm.t00z.medium_range.channel_rt.f006.conus.nc","c:/users/nt/desktop/nwm.t00z.medium_range.channel_rt.f006.conus.nc")
  temp = nc_open("c:/users/nt/desktop/nwm.t00z.medium_range.channel_rt.f006.conus.nc")
  </code></pre>