Asymmetrical error bars in line-plot

I want to display asymmetrical error bars in a line plot with two lines “verum” and “sham”.
In the grid values for the lines (specify as y) are each followed immediately by - and + values for the error bars (specify as E-/+).
However in the generated plot, both lines have the same values for the error bars, i.e. those following the first y-variable “verum”.
The error bar levels following the second variable “sham” are obviously not used.
Please advise.