title: Exporting ggplot2 grid to PDF error: 'Error in grid.Call.graphics... invalid font type'
body: <p>I was wondering if any of you have encountered the following issue: When I attempt to export a plot to PDF in order to retain transparencies using the following code:</p>
  
  <pre><code>    f &lt;- function(x) {
    ans &lt;- boxplot.stats(x)
    data.frame(ymin = ans$conf[1], ymax = ans$conf[2], y = ans$stats[3])
  }
  
  RTs.box = ggplot(mean.vis.aud.long, aes(x = Report, y = RTs, fill = Report)) + theme_bw() + facet_grid(Audio~Visual)
  RTs.box + 
  
  geom_boxplot(outlier.shape=1 ) + geom_hline(yintercept = .333, linetype = 3, alpha = .8) + theme(legend.position = "none") + ylab("Reposponse Times ms") + scale_fill_grey(start=.4) +
  labs(title = expression("Visual Condition")) + theme(plot.title = element_text(size = rel(1)))+
  theme(panel.background = element_rect(fill = "grey90"), panel.grid.minor = element_blank())+    stat_summary(fun.data = f, geom = "crossbar", 
              colour = NA, fill = "white", width = 0.75, alpha = .9)+
  geom_boxplot(fill = "transparent", outlier.shape=1)+
  theme(axis.title.y = element_text(vjust=0.5)) +
  theme(axis.title.x = element_text(vjust=-0.5)) +
  theme(text=element_text(size=30))+
  theme(axis.title.x=element_text(size=40))+
  theme(axis.title.y=element_text(size=40))+
  theme(plot.title = element_text(size = 40, vjust=1))+ #vjust respositions text
  coord_cartesian(ylim = c(0, 3000))+# This allows clipping of plot without dicarding data in analysis
  scale_y_continuous(breaks = (seq(0,3000,by = 500)))+
  theme(axis.text.y =element_text(size=17, (hjust=-.5)))+ # THIS CHANGES SIZE OF VALUES ON Y-AXIS
  theme(panel.margin = unit(1.2, "lines"))# moves panels further apart
  </code></pre>
  
  <p>I get the following error:</p>
  
  <p><img src="https://i.stack.imgur.com/eBNlm.png" alt="enter image description here"></p>
  
  <p>'Error in grid.Call.graphics... invalid font type'</p>
  
  <p>The image does save as a PDF BUT all the axes text has NOT been saved.</p>
  
  <p>I've tried importing library(extrafont) but get the same error regardless of what font I use.</p>
  
  <p>Have any of you experienced this problem before &amp;/or do you have any suggestions on how to solve it?</p>
  
  <p>Thanks as always.</p>
  
  <p>Edit:</p>
  
  <p>Here is some example data for mean.vis.long:</p>
  
  <pre><code>Visual              Audio            Report  subject_nr    RTs
  Right Circle 1st    2 Central Beeps  Right   10            717.6936
  Right Circle 1st    Left Beep 1st    Left    10            540.0408
  Right Circle 1st    1 Central Beep   SIM     10            540.0408
  Right Circle 1st    No Beep          Right   10            717.6936
  Right Circle 1st    Right Beep 1st   Left    10            540.0408
  Right Circle 1st    Left Beep 1st    SIM     10            540.0408
  Left Circle 1st     2 Central Beeps  Right   10            717.6936
  Left Circle 1st     Left Beep 1st    Left    10            540.0408
  Left Circle 1st     1 Central Beep   SIM     10            540.0408
  Left Circle 1st     No Beep          Right   10            717.6936
  Left Circle 1st     Right Beep 1st   Left    10            540.0408
  Left Circle 1st     Left Beep 1st    SIM     10            540.0408
  Left Circle 1st     2 Central Beeps  Right   10            717.6936
  SIM Circle Pres     Left Beep 1st    Left    10            540.0408
  SIM Circle Pres     1 Central Beep   SIM     10            540.0408
  SIM Circle Pres     No Beep          Right   10            717.6936
  SIM Circle Pres     Right Beep 1st   Left    10            540.0408
  SIM Circle Pres     Left Beep 1st    SIM     10            540.0408
  </code></pre>
  
  <p>There are 3 Visual conditions: Right Circle 1st; Left Circle 1st SIM Cirlce Presentation.</p>
  
  <p>There are 5 Audio conditions: 1 Central Beep; 2 Central Beeps; Left Beep 1st; Right Beep 1st; No Beep.</p>
  
  <p>And there are 3 report options: Left; Right; SIM.</p>