Hi
I see that you used OGS5.7; please add it as a keyword and/or in the title so that the concerned experienced users spot it.
It will be good if you could provide all the input files of the model setup. This will help the experienced users on the forum to identify the problem, as it may not necessarily lie in the krc-file.
The solution is not converging at what looks like the boundary nodes. It could be related to the time step that you use, which may or may not be suitable to the velocity, rate constants etc. Have you double checked that all the parameters are correct with consistent units, aligned with your conceptual model? What about the initial conditions and boundary conditions - there seem to be several warnings regarding the assigned values?
Good luck!
Swamini