title: Loading Data.Table and dplyr one after other gives errors
body: <p>I ran into a problem that I have not encountered before. When I load the <strong>data.table package (version 1.9.4)</strong> alone, and then try to subset a dataset to remove a variable I get no issues. However, when I load <strong>plyr (version 1.8.2)</strong> and <strong>dplyr (version 0.4.1)</strong> as well, I get the following error (tried the same with a toy dataset as well). Note that the original file is in Excel and I use library(readxl) to read the file into a RData file format (the file,<strong>vahere.RData</strong> is available here <strong>(<a href="https://goo.gl/kzI5bD" rel="nofollow">https://goo.gl/kzI5bD</a>)</strong>. The file as three variables - LINK_ID (numeric), TMC (character), MPORegion (character). The error I get is:</p>
  
  <pre><code>Error in `[.tbl_df`(x, r, vars, with = FALSE) : 
  unused argument (with = FALSE)
  </code></pre>
  
  <p>I don't remember encountering this error before. If anyone has any insights on what is going on I would really appreciate it. I tried it on two separate machines (Windows 7) and get the same error. The Sys.Info from both machines are below:</p>
  
  <pre><code>Machine 1 - sysname "Windows", release "7 x64", version "build 7601, Service Pack 1", machine "x86-64"
  Machine 2 - sysname "Windows", release "7 x64", version "build 7601, Service Pack 1", machine "x86-64"
  </code></pre>
  
  <p>Below is the history of the run.</p>
  
  <pre><code>&gt; library(data.table)
    data.table 1.9.4  For help type: ?data.table
    *** NB: by=.EACHI is now explicit. See README to restore previous behaviour.
  &gt; load("vahere.RData")
  &gt; vahere[is.na(vahere)] &lt;- "RestofVA"
  &gt; vahere &lt;- setDT(vahere)
  &gt; 
  &gt; # Drop link id and identify unique tmc to region
  &gt; uniqtmcs &lt;- subset(vahere,select=-c(1))
  &gt; library(plyr)
  &gt; library(dplyr)
  Attaching package: ‘dplyr’
  The following objects are masked from ‘package:plyr’:
  arrange, count, desc, failwith, id,
  mutate, rename, summarise, summarize
  The following objects are masked from ‘package:data.table’:
  between, last
  The following object is masked from ‘package:stats’:
  filter
  The following objects are masked from ‘package:base’:
  intersect, setdiff, setequal, union
  
  &gt; rm(vahere)
  &gt; load("vahere.RData")
  &gt; vahere[is.na(vahere)] &lt;- "RestofVA"
  &gt; vahere &lt;- setDT(vahere)
  &gt; 
  &gt; # Drop link id and identify unique tmc to region
  &gt; uniqtmcs &lt;- subset(vahere,select=-c(1))
  Error in `[.tbl_df`(x, r, vars, with = FALSE) : 
  unused argument (with = FALSE) 
  </code></pre>