Unrevoked: Is my firmware too new?
One click root methods use a simple rootkit exploit package to gain root permissions to the Android kernel. Once this is done, they modify file permissions to make the rooting permanent.

These exploits have been patched by Google and device manufacturers for a long time now, and the vast majority of one click rooting solutions are outdated and no longer work.

In other words - your firmware is too new. It has been patched against rootkit exploits.