A forgotten symbolic expression can cause this message:

Fix this by replacing the symbolic with an independent variable :

A verification process evaluates the coefficient at a point inside the simulation domain. Should this evaluation point be, for example, at a singularity of the coefficient, then the coefficient is rejected.

Set up a coefficient that has a singularity at :

For a one-dimensional mesh with bounds from 0 to 1, the verification coordinate happens to be at . The coefficient is singular at the verification coordinate for this region:

Change the verification data such that the test coordinate is not at the singularity of :

More information can be found in the options section of InitializePDECoefficients.

For nonlinear equations, the default initial seeding is 0. This can conflict with some equations:

Note that the heat source term has a term. When the initial seed is set to zero, this will fail. The solution is to use a nonzero initial seed: