Calculating the magnetic field inside a closed loop of wire

[aftershock]

Homework Statement

I basically have a closed loop of wire with a current flowing through it clockwise. I need to determine the magnetic field in the center, along the z-axis.

Homework Equations

Ampere's Law and Biot-Savart Law

The Attempt at a Solution

Using Biot-Savart Law I actually pretty easily calculated the field and it was correct. (sorry for not typing out formulas but the math symbols seem to be giving me trouble and I don't think I need to).

But if I use Ampere's law, then as soon as I place an amperean loop in the middle of the wire the I enclosed is 0, leading me to believe there should be no magnetic field within the wire. How am I using Ampere's law wrong?

 

[zhermes]

What direction is the magnetic field going at the center of the wire-loop?
And just because there's no current enclosed doesn't mean there's no magnetic field... just no net field along (and in the direction of) the amperian loop.