Solve block issue with Mathcad 15, works in Mathcad prime 3.0

Hello,

I need to solve a system of simultaneous equations to find reference parameters for a PV model. I have entered the same set of equations in Mathcad 15 and Mathcad prime 3.0. As far as I can see the equations are exactly the same in both worksheets. The problem I'm having is that Mathcad 15 is not returning an answer although I get a solution in Mathcad prime 3.0. I would like to resolve the issue in Mathcad 15 as I need to plot graphs and do some further analyses using functionality that is available in Mathcad 15 but not prime. I also have no way of telling which algorithm Mathcad Prime  3.0 applied to return the solution so I can't even replicate that in Mathcad 15.

I also noticed that if I change the guess values in prime and then change back to original guess values that returned a solution, sometimes mathcad prime 3.0 doesn't return a solution also, no idea why.

(Note that for a valid solution 1<a<2 but when I include this constraint mathcad prime 3.0 won't return a solution even though the solution it gives initially meets this constraint)

Any assistance to resolve this will be greatly appreciated!!!