Plasma Module Error: Failed to Evaluate Variable Jacobian

I am attempting to model a DC microdischarge in Argon using COMSOL 4.2. I am using a 2D axisymmetric model. The top layer is the anode, the middle layer is a dielectric and the bottom layer is the cathode. The small triangular section is the micro-cavity. The rest is the 'chamber', consisting of Ar.

I've imported all the necessary cross sections as well as townsend coefficients from another physics interface. I have defined my materials properly (resistivity data on the anode and cathode, and permittivity data on the argon).

I've checked and re-checked my BC's and my materials, but despite it all I can't figure out why I get:

Failed to evaluate variable Jacobian:

- Variable : mod1.dc.sfluxi_wAr_1p
- Geometry: 1
- Boundary: 14

I understand the Ar_1p is COMSOL's notation for Ar+. However, I can't locate the variable 'sfluxi_wAr_1p'. The boundary number refers the anode region contiguous to the microcavity.

I've attached my model.

Any help will be greatly appreciated.