Two problems:
1. Up in the top, you have defined a value for F.02. The GPa as its unit is a type 'Constant' instead of 'variable'. But potentially that's not a problem for Mathcad 15.
2. Down at the bottom, you provide a guess value for lambda. That must have the correct unit, Pa^3. If you add that, the solve block at least finds the lambda value for x and y both 1 m. But for other values of x and y (guided by the CreateMesh function) no suitable lambda was found. You may need to provide a better guess value for lambda. This is what I get with a mesh of 10x10 points, and a guess value of -10 MPa^3 for lambda:

And with a guess value of -50 MPa^3 and 20x20 points, it shows that there are 2 points where lambda produces totally different values:

I'll leave it to you to investigate that.
Success!
Luc