How to eliminate problems like "Matrix is close to singular or badly scaled" in Simulink Model?

I am currently modelling a distribution circuit (with Variable load profile, PV injection and On load Tap Changer(OLTC)) to get an insight on effects of PV on distribution circuit. I was able to run the entire model successfully without OLTC. As soon as I connected the OLTC (detailed model given in OLTC example) I got 3 warning messages "Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND =3.076991e-19." and results were totally incorrect. I then altered the transformer parameters to make it an ideal transformer (with R= 0.0001 and X = 0 - in all R,X fields) then I was left with 1 warning but the results were nearly correct.

Now I want to model the transformer impedance and eliminate the 1 warning that is coming. So can anyone tell me why SIMULINK model is behaving weirdly on insertion of impedance? Any way to go about the problem?

For information: 1) I tried OLTC phasor model in library (not working for me correctly so I used detailed model in example). 2) I tried to put separate series impedance with transformer, it also didn't work. 3) Using Simulink and Simpowersystems