output Resultypes

Hi all,
I have a problem when run Plaxis by python code as follow:
in the output Plaxis I run the code

for step in g_o.Phase_3.Steps:
Xcoor = g_o.getresults(step, g_o.ResultTypes.Soil.X, 'node')

The output in Plaxis appear a notification

!!!!> getresults Step_7 ResultTypes.Soil.X "node"
Invalid step or phase. Phase has not been previewed or calculated yet.

I do not understand the problem, because I run Plaxis and I also can show results in Plaxis Output, but I can not export they to .txt by python script.
thanks a lot