I am encountering a problem when I use the function Manipulate. Even when I run the simple code
f[a_,x_]:=a*x Manipulate[Plot[f[a,x],{x,-1,1}],{a,1,2}] I obtain
I have tried to reset the Kernel, restart the computer, and also increase the time for returning this error message to 90s -- Anything does not work. Any thoughts?
Importante note: I should say that if I go to the examples of Mathematica in the Documentation Center, the Manipulate works

