Singular matrix, returned solution not converged

Hi,

I have a Matlab code that solves four coupled differential equations, which works and gives me the attached plot. (The actual code is here: www.ee.ucl.ac.uk/~rjames/modelling/constant-order/oned/, scroll down to "lc3k.m" along with a description of the problem if you want more details.)

Now I try to reproduce it in COMSOL. I have attached my attempt. This is my first time using PDE interfaces in COMSOL.

First I put the equations under Model 1 > General Form PDE. I have double checked these are typed correctly, and they come straight from the matlab code.

Next I put the boundary conditions (Dirichlet conditions at x=0 and at x=1, same as the Matlab code) under Model 1 > General form PDE > Initial values. These guesses are pretty close to the solution so I don't think that's the problem.

Next I click Solve and find:
"Failed to find a solution. Singular matrix. Returned solution is not converged."

I've tried using various different solvers and don't know what else to try. Can someone tell me how to pinpoint the problem, or, an example of solving coupled 1D differential equations?

Thanks!