求助，附代码，数据，谢谢
   数据链接：https://pan.baidu.com/s/1coP5UY


代码：
a <- read.table("final2016.csv",header=TRUE,sep=";",fileEncoding="GB2312")#Mac OS 环境下，要sep＝";"
a$NO <- as.character(a$NO)
a$papername <- as.character(a$papername)
a$posttime <- as.Date(a$posttime)
a$paperlink <- as.character(a$paperlink)
#a$count_of_read_NO. <- as.numeric(a$count_of_read_NO.)
library(ggplot2)
qplot(posttime,count_of_read_NO.,data=a,geom="point",colour=repost,size=6)



为什么会出现下列错误信息，该怎么办？
Error in `$<-.data.frame`(`*tmp*`, "papername", value = character(0)) :
  replacement has 0 rows, data has 400