使用RStudio/knitr编译PDF的错误

Posted this on RStudio help already but seeing if anybody here has any idea. I'm getting the following error below when I try to Knit PDF with a plot in the document using RStudio. The error does not occur when I try to Knit PDF without a plot nor does it occur when I Knit HTML with the plot. I'm on a Mac with Yosemite.Posted this on RStudio help already but seeing