Thread: Unknown C ESP function call error message

Help!

I keep getting the following message after completeing a function call and returning to the main subroutiney but bombs before I can choose to exit the program:

Error:
The value of ESP was not properly saved across a function call. This is usually the result of calling a function declared with one calling convention with a function pointer declared with a different
calling convention.
******************* END OF ERROR MSG ****

Code is simple, error occurs after running the largeNumber function below and after the program has returned. Note: the largeNumber function has not receiving or sending values.

Code:

#include <stdio.h>
#include <ctype.h>

char getMenuOption (void);
void largestNumber (void);
void diamond (void);

int main (void)
{
	char  enterKey;
	char  menuOption;

	do
	{
	    menuOption = getMenuOption();
		switch (menuOption)
		{
			case 'D' :  diamond ();
				break;

			case 'L' :  largestNumber();
				break;
						
			default  :  printf("\n\n***** GOODBYE *****\n");
		}

		printf("\nPress [Enter] to Continue ");
		scanf("%2c", &enterKey);
		
	}
	while (menuOption != 'Q');

	return 0;
}

void largestNumber (void)
{
...... code .......

return;
}