This is very far from a minimal example. I also do not get the error message that is in this issue, but:
Solving nonlinear variational problem.
Traceback (most recent call last):
File "mwe_old.py", line 139, in <module>
Solver.solve()
RuntimeError:
*** -------------------------------------------------------------------------
*** DOLFIN encountered an error. If you are not able to resolve this issue
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*** fenics-support@googlegroups.com
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*** Remember to include the error message listed below and, if possible,
*** include a *minimal* running example to reproduce the error.
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*** -------------------------------------------------------------------------
*** Error: Unable to solve linear system using PETSc Krylov solver.
*** Reason: Solution failed to converge in 0 iterations (PETSc reason DIVERGED_PC_FAILED, residual norm ||r|| = 0.000000e+00).
*** Where: This error was encountered inside PETScKrylovSolver.cpp.
*** Process: 0
***
*** DOLFIN version: 2019.2.0.dev0
*** Git changeset: f0a90b8fffc958ed612484cd3465e59994b695f9
*** -------------------------------------------------------------------------
I would strongly suggest that you try to reduce the complexity of your problem, and have a look at Default absolute tolerance and relative tolerance - #4 by nate