Axisymmetric indicates that the domain is axisymmetric about the x axis. When Axisymmetric is enabled, the 2D axisymmetric form of the governing equations is solved instead of the 2D Cartesian form. (This option is available only when you start the 2D version of the solver.)

It is important to note that while the assumption of axisymmetry implies that there are no circumferential gradients in the flow, there may still be non-zero swirl velocities.

For axisymmetric, the axial direction should be x and radial is positive y. Even if the y starts with -1e-32, it will fail.

Do a Mesh->Check to make sure you don't get

Checking for nodes that lie below the x-axis.

WARNING: Invalid axisymmetric mesh: 6 nodes lie below the x-axis.

and

WARNING: Mesh check failed.

If you do,

Use Mesh->Translate and move the geometry so ymin is +ve.

Be sure to change the zone type of the axis of rotation to "axis" and not symmetry, using the Boundary Conditions task page.