Issue with CAS solver function involving passing strings to the variable position.

[Gene222]

You might have a problem with the names you used for your variables. See the following posts below.
HP Prime Solver Variables Issue
Programming solve function

I also have had problems with expressions that included trig functions that gave multiple answers, where I had to either use an initial guess that would narrow the search for a solution, or put a limit on the solve variable such as 0.0001..2*pi.

I also had problems where the variables would give a division by zero error or where the change in the parameter variables would not significantly change the solve variable, so that fsolve could not find a solution. In one case, I ended up replacing fsolve with a trial and error/bisection method in order to find a solution.