Constant contact angle boundary condition
 

I am trying to solve the generic transport equation for diffusion only, on a four-sided geometry. I am using a User Defined Scalar for the property for which it is to be solved. I want to implement a constant contact angle boundary condition without using the VOF model on one of the boundaries. I have a UDM for the contact angle, which I want to use as a boundary condition. The contact angle is given by acos(-x*C_UDSI_G(c,t,0)[0]-y*C_UDSI_G(c,t,0)[1]). But how do I implement it in F_PROFILE? Fluent crashes every time I use C_UDSI_G (Gradient function) in DEFINE_PROFILE macro.