Poission's ratio problem related to Structural Mechnics

Dear all,

I just started to learn COMSOL and tried to conduct a simple simulation of deformation of an elastic plate by a face load. I used Solid Mechanics model in 4.3 edtion.

1. When I set the material property, poission's ratio as 0.3, the simulation worked well and I could check the deformation plot. But when I change the ratio to 0.5, the problem came. It said,

- Detail: Undefined value found in the equation residual vector.
.There are 4885 degrees of freedom giving NaN/Inf in the vector for the variable mod1.u
. at coordinates: (-0.01,-0.005,0.0002), (-0.01,-0.005,-0.0002), (-0.01,-0.005,0), (-0.01,-0.00426971,-0.0002), (-0.01,-0.00463486,-0.0002), ...
There are 4885 degrees of freedom giving NaN/Inf in the vector for the variable mod1.v
. at coordinates: (-0.01,-0.005,0.0002), (-0.01,-0.005,-0.0002), (-0.01,-0.005,0), (-0.01,-0.00426971,-0.0002), (-0.01,-0.00463486,-0.0002), ...
There are 4885 degrees of freedom giving NaN/Inf in the vector for the variable mod1.w
. at coordinates: (-0.01,-0.005,0.0002), (-0.01,-0.005,-0.0002), (-0.01,-0.005,0), (-0.01,-0.00426971,-0.0002), (-0.01,-0.00463486,-0.0002), ...

No matter how I change other parameters, like load value or mesh, it always got wrong. But the 0.5 is the one I really need. Hope someone could help me figure out the reason.

2. And there's another question. when I changed the value of load to the surface and compute for result, I found the plot didn't change. I mean in reality, when the load increases, the displacement should be also increased. But in the plot, the shape of plate is never changed. Is this problem related to scale ratio or something?

Here I attach my mph and I really appreciate the help!