empty character constant error

Can someone tell me what this error means and how can I fix it. I know it has to be something simple that I am overlooking. I have included the part of my program that contains the error:

Code:

void NameFind(string carName[], string workOrder[], string mechanic[], int count, char let)
{
	int a;
	int b=0;
	cout << "\nCars with last name beginning with" << let << ":\n";

	for(a=0; a<count; ++a)
	{
		if(carName[a].find(toupper(let)) ==0)
		{
			cout << "\nCar name:" << carName[a] << '' << "Work order:" << workOrder[a] << '' << "Mechanic:" <<mechanic[a];//error appears in this line????
			++b;
		}
	}
	if(b==0)
		cout << "There are no cars whose last name begins with " << let <<". \n";
}

try replacing ' ' with " "