lsolve Function: Undefined Variables

Hi everyone,

I am currently trying to design a framework by carrying out the Method of Joints and checking all forces on Mathcad.

I have managed to get all calculations, however, when I input it into Mathcad, it came up as an error:

"This calculation does not converge into a solution"

I have attached the file and I would appreciate it if someone could tell me what the problem is.

Thanks for your help in advance.