title: Scale_fill_brewer in geom_bar
body: <p>I am trying to use scale_fill_brewer in a barplot(geom_bar), but I am having always the same error that I don't understand.
  Here, that would be my code:</p>
  
  <pre><code>LW25_cwt &lt;-data.frame(
      "name"=c("N","NE","E","SE","S","SW","W","NW","C","A","U"),
      "days/winter"=c(7.07,3.6,8.4,5.5,10.5,6.2,7,4,54,43,10)) 
  LW10_cwt &lt;-data.frame(
      "name"=c("N","NE","E","SE","S","SW","W","NW","C","A","U"),
      "days/winter"=c(2.07,1.6,3.4,6.5,11,6.7,7.2,10,51,42,4))
  
  
    LW25_cwt$LWdays &lt;- "LW25"
     LW10_cwt$LWdays &lt;- "LW10"
     sp=rbind(LW25_cwt,LW10_cwt)
  
  
     c2 &lt;- ggplot(sp, aes(y=days.winter,x=name, fill=LWdays)) + 
          ggtitle("LoW-Wind days (1961-2000)") + 
          theme(plot.title = element_text(lineheight=1,face="bold", color="black",
          size=17,vjust=2.5))+     
          ylab('days/year') +  xlab('CWTs Types') +
          geom_bar(stat="identity", position="dodge") 
     c2 &lt;- c2 + scale_fill_brewer(palette="Set2")
  </code></pre>
  
  <p>If I don't use scale_fill_brewer, it perfectly works, but if I use it I have this:</p>
  
  <p>Error in object[seq_len(ile)] : object of type 'S4' is not subsettable
  In addition: Warning messages:</p>
  
  <pre><code>1: In class(y) &lt;- class(x) :
    Setting class(x) to multiple strings ("brewer", "discrete", ...); result will no longer be an S4 object
  2: In class(y) &lt;- class(x) :
    Setting class(x) to multiple strings ("brewer", "discrete", ...); result will no longer be an S4 object
  </code></pre>
  
  <p>Any idea?? I have been looking it, but unfortunately I have not found the solution.</p>