Error in knitting bar plots, anova tables etc.

Hi, im fairly new to RCMDR, RSTUDIO etc. However, i have attempted to run some bar plots and effect plots of a model I am analysing. When i come to Knit the work to PDF or HTML i recieve an error message which states

" Error in Barplot(PovertyOrdered, xlab = "PovertyOrdered", ylab = "Frequency", :
could not find function "Barplot"
Calls: ... eval -> eval -> with -> with.default -> eval -> eval
Execution halted"

I have gone through and installed a few packages in an attempt to rectify this message yet I can't find one which will give me bar plots. I have removed the line from the document and attempted to knit and the message pops up for other codes I will be running too, such as an Anova table.