Good on you! If you have a look at your structure, you really only have symmetry in the YZ plane (which is what you fixed it to). Setting symmetry for XZ plane gives you the error as you mentioned in your post, because your port is not in the calculation domain. When you define one symmetry plane, your structure basically cuts in half for that plane (solver only calculates half of your structure and assumes the other side of your symmetry is identical).
When you define XZ symmetry plane, you have your port on one end, but not the other. Therefore it is not symmetrical.
Another thing to note: Apart from the waveguide port defined, there really isn't symmetry in the XZ plane due to the microstrip feed line. I added this comment because if you happen to feed your patch with a coax in the center of patch, but do not have symmetry in the plane you are defining, the error message will not show and you will definitely get unexpected results. Worse yet, receiving wrong results thinking they are right!
Hope that helps and all the best!