Help!!

I ran a simple flow simulation of flow inside a rectangular channel; flow simulation went fine with no error, and I was able to do a Surface Plot of shear stress on the bottom plate of the channel.
I am now trying to obtain those shear stress values at certain coordinates on that bottom plane and export it to excel, so I did Point Parameters and chose a few points on that plane. However an error message came up: "No parameters can be evaluated. Please check selected points or parameters."  -- even though clearly the Surface Plot shows some finite values of shear stress.

Any idea why this occurs / what the solution is?