Dear Neal,
thank you for your comment. I have now set the precision of all of my coefficients to 20 with SetPrecision[x,20], where x is a given coefficient. This indeed overcame problem nr. 4 in my message above. However, I am still left with an unsolvable stiff system, even if I impose WorkingPrecision->19. I will try increasing further the precision of my coefficients and setting a higher working precision. Also, I can try to modify my equation system, I suspect there might be steep chages in some derivatives that I can try to avoid. Cheers, Vanni
