GPL-only symbol Error

Hi All, Basically, I am developing a kernel module named "xyz.ko" and my MODULE_LICENSE is "Proprietary". I have got an error "GPL-incompatible module xyz.ko uses GPL-only symbols". I am having trouble identifying it. How to avoid this error in during MODPOST?. Is there any way to avoid this error? Can you someone throw light on this. Regards, S. Sengottuvelan.