qPCR standard curve problem - (Jun/15/2008 )

I am doing standard curves on cDNA (also ChIP input).
I am using primers that previously gave great standard curves and continue to give other
people good standard curves.
However, when I dilute my material 2x, and 4x I see no difference in cts! After that the 8x and 16x points look and little better. Sometimes my 2x and 4x dilutions actually give me lower ct values (increased signal).
How is this possible?
Thanks for any insights.

i would say that you have some PCR inhibitors in your sample.