Datenum problem with errorbar plot

Hello all,

I have an issue displaying datenum data in a plot. I want to use the errorbar plot function to shot date against Temp, howver errorbar doesn't agree with datetime value's, however when I convert to datenum (as shown below), my first two points are the wrong side of January as shown in the image, they should be the last two points in december.

weeks = datenum(Date_ave);

errorbar(weeks,Temp_ave,Temp_sd,'-s')
datetick('x','mmm','keepticks')