Micro-Cap is so much better than LTspice. Yet, Micro-Cap has one flaw: its propensity for erroring with the message: "Matrix is singular". This means that whenever Micro-Cap performs matrix algebra upon an approximation of your circuit, it comes up with a symetrical matrix which is incomprehensible as an evaluation. It must remain non-symmetrical to retain any meaningfulness to the simulator.

Hence, there is a simple remedy: place small resistances throughout your circuit, in between each component, to represent solder joints and vary each resistance ever so slightly.

Solder joints would never be perfectly of the same resistance anyway. So, why not give the simulator something arbitrary to be happy with?

What I do, is assume that I am a non-skillful solderer (which I am!) incapable of soldering a joint with anything less than around 100 milli Ohms of resistance. I position these resistances throughout my circuit. And, then, I vary each one - alternately up or down - by one milli Ohm in a symmetrical manner (although randomized may be better?). So, one resistance will be 99 milli Ohms while the next resistance in series from its neighbor will be 101 milli Ohms. This seems to prevent this sort of Micro-Cap error from ever arising to ruin my day!