comsol error failed to evaluate variable

Hi,

i am trying to design spiral inductor using the physics "magnetic and electricfield(mef)
but i have this error

Failed to evaluate variable
- Variable : mf.normB
- Geometry: 1
- Domain: 2 3 4 5 6
failed to evaluate expression
expression:mf.normB
plot:mscl(multislice)

see the attached file.

Can any one help me, please ?

thanks.