Help with solve blocks

I wasn't sure if I should post this in the calculus or algebra section as it pertains to both... I have a solve block set up that set's the function, the derivative wrt a variable, and then two other combinations equal to 0. I have 4 variables I am solving for. However, my solve block doesn't seem to work. Oddly enough, if I simplify the functions with my boundary conditions, and then just copy and paste into a new solve block, setting them equal to zero, it works. I don't understand what it is I'm doing wrong. Any help would be greatly appreciated. I've attached a copy of the sheet I'm working on.