Immunopreciptation

[Wun Chey Sin]

Dear netters,
I have difficulty in immunoprecipitating protein from PC12 cell lysate using polyclonal antibodies.  The antibodies definitely work on the western .  I have been doing DNA work and have no experience in protein work. Is there any things to take note 
tricks.  What is the most likely reason?  (  The buffer contains the usual NaCL and inhibitors and 1% triton X)

Thanks
Wun Chey