Inconsistent units in a hyperelastic material model

Hi,

I am trying to create a user defined hyperelastic material model. For the isochoric strain energy density (Wsiso) I defined two different terms, Wf and Wm in the following way:

Wf = (1/2)*(c1/c2)*(exp((c2*(sqrt(i4)-1)^2))-1)

Wm = (u/2)*(i1-3)-u*log(sqrt(i3))

c2, i4, i1, and i3 are unitless

c1 and u have the unit [MPa]

In the variable section I can see that COMSOL displays Wf as having the unit [Pa] (which is expected) but Wm has the unit [m]. Since Wsiso = Wf+Wm, I get a error message saying "Inconsistent unit" because Wf is in pascal and Wm is in meters.

It surprises me that Wm is in meters since it only contains the variables u [Mpa] and i1, i3 [unitless]. Looking at the equation the expected unit would be [Pa].

Can anyone help me with this problem

Thanks in advance,
Brynjar