I used ggplot2 for drawing my bar plots and after adding geom_errorbars I get many error bars stacked on each other (picture below).

What's the problem? I tried to draw it both in Windows and Linux to make sure the problem is not from my R version, and I got the same results.

ggplotf.tm,aes(Gene,Expression,fill=Group)) +
  geom_bar(stat="identity", position=position_dodge())+
  geom_errorbar(aes(ymin=Expression-sd, ymax=Expression+sd), width=.2,
                position=position_dodge(.9))