insmod: error inserting 'test2.ko': -1 Unknown symbol in module

Hi, What is basic reason behind error "Unknown symbol in module" ? I have two modules test1.ko and test2.ko. test1.ko loads succesfully but test2.ko gives error insmod: error inserting 'test2.ko': -1 Unknown symbol in module dmesg shows all symbols in module as unknown. To give more details I have compiled both modules same way with same compiler options and with modpost, Module.Symvers files. Another point to mention is that both modules load perfectly on 2.6 kernel. But kernel on which I am trying is 3.0 series kernel. What can be entry point to look into this issue ? Thanks, Pritam