Python output, missing result

Hi guys,

I tried to use Python scripts to select a node and want to retract the Utot of this node for all steps and phases. 

Here is how I selected the node

output_port = g_i.selectmeshpoints()
s_o, g_o = new_server('localhost', output_port, password='123456789')
g_o.addcurvepoint('node',(0,0),(1,0))
g_o.update()

And then I used the code posted in the forum to retract the Utot

u.append(g_o.getcurveresults(g_o.CurvePoints.Nodes[0],
step,
g_o.ResultTypes.Soil.Utot))

But I got error message 

PlxScriptingError: Unsuccessful command:
not found
There are missing result(s). Either the project isn't calculated or the result type isn't available in this phase or step.

Wondering how to fix this?

Thanks in advance!