Warnings when doing phase noise performance in ADS

when simulating phase noise performance in ADS as in the example shown in this tutorial
http://www.odyseus.nildram.co.uk/Sys...PhaseNoise.pdf
i receive this warnings:
"Warning detected by HPEESOFSIM during HB analysis `HB1'.
In `HB_NOISE', a noise node was requested where
NoiseNode[0] = `PNoise_OL' is not a legal node name.
Warning detected by HPEESOFSIM during HB analysis `HB1'.
No noise to simulate for NoiseCon `HB_NOISE'
Warning detected by HPEESOFSIM during circuit set up.
Unable to resolve variable(s) or functions(s) in expression ' PNoise_OLout=real(PNoise_OL[0])'
PNoise_OL"
why is the node name illegal? i could change it to another one but i want to know what is the reason of the warning as the name is used in the tutorial
regards