I suspect that the reason is that sin and cos are existing functions and you don't use them like that. Below demo code does not throw the error that you have.

void setup()
{
int V = 140;
int Vx = (V * sin(3.14));
int Vy = (V * cos(3.14));
}

void set()
{
int V = 140;
int Vx = (V * sin(3.14));
int Vy = (V * cos(3.14));
int FRW = (Vx + Vy);
int FLW = (Vx - Vy);
int BLW = (Vx + Vy);
int BRW = (Vx - Vy);
}

Since sin(PI) and cos(PI) are known values (0 and -1) you could skip the math and just use:

int FRW = -V;
int FLW = V;
int BLW = -V;
int BRW = V;

Did you, perhaps, ever want to travel at an angle other than 180° (Pi radians)? If so, you should translate the angle to radians (angle * PI/180) and pass that to sin() and cos().