Let me guess. You have defined t to be a symbolic variable?
You can verify that using the whos command. Thus, if I do this:
syms t
whos t
Name Size Bytes Class Attribute
t 1x1 8 sym
So t is symbolic, as you see above.
I can use sin(t), because the symbolic toolbox can work with the sin function. However, square is a function from the signal processing toolbox. It REQUIRES double precision inputs. Therefore, you get an error message.
Not all functions are defined for symbolic input.
