If you don't define any boundary conditions (in which case, things default to dA/dn = 0), the problem can only be solved if the currents in the domain sum to exactly zero. Subsequently, if the currents don't add up to exactly zero, the solver will hang when boundary conditions are defined. The "cure" is to define A=0 on the outer boundary of the solution domain (or use one of the "open" boundary condition strategies described in Appendix C of the manual). If some boundary conditions are defined, the solution will be uniquely defined and the solve won't hang.Trying to use areas with current densities with cross sectional areas is problematic if you don't get the areas for plus and minus to match. The simulator seems to hang if you don't get exact matches for return currents. Point currents are much easier to deal with.