Error detected by hpeesofsim during netlist flattening.

hi all,

I have this below error while simulating my design in ADS during usage of 130nm library files.
Simulation / Synthesis Messages

Error detected by hpeesofsim during netlist flattening.
`M1' is an instance of an undefined model `pmos_rf'.

Status / Summary


hpeesofsim (*) 350.500 Feb 19 2009 (built: 02/19/09 22:31:44)
Copyright Agilent Technologies, 1989-2008.
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Simulation terminated due to error.
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Plz anyone help me to solve this problem....