Purbasha,

1 - The BuildFEMatrix module indicates that your mesh has negative Jacobians.  If this is truly the case, the module cannot function as it was written to do and your assigned conductivities within the space will not be correct.  You can check to see if you have any negative Jacobians by using the GetMeshQualityField module and selecting Jacobian in the UI options.  Attach a ReportFieldInfo to this and look at you min/max values.  You should have nothing less than 0.  You might be able to fix this with the CleanUpTetMesh module, though when I just tried, it did not remove all negative tets.

2 - The nodes that you sent are not actually within the volume.  The appear to not even touch the volume, therefore, any potential value that you apply to these electrodes will not be able to influence the axon.  I've attached a picture below (green orbs are your electrode sites blue are projections of the electrodes onto the mesh nodes).  These nodes are (as the error message suggests) out of range.  Try to project the nodes to the surface.  You can try using the ProjectPointsOntoMesh module to see if that works once you have confirmed that your mesh has no negative jacobians.

Hope that helps,