IP planning function variables not available in DS 1.5 SP1

Hello design studio pros,

I am trying to pass variable values to a planning function in DS 1.5. SP1

The variables are placed in the parameter section of the copy planning function:

copy from 0version "P_VERSION_FROM"

to version "P_VERSION_TO"

the two variables are not available when I edit the script

    // plan from version

    PF_VERSION_COPY.setVariableValueExt("P_VERSION_FROM", DROPDOWN_2.getSelectedValue());

    // plan to Version

    PF_VERSION_COPY.setVariableValueExt("P_VERSION_TO", DROPDOWN_2.getSelectedValue());

when I execute the script, DS throws an error message.

Has any of you had the same problem and solved it?

kind regards, Thomas