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;
}

---

> scanf("%2c", &enterKey);
This is one instance of where you're going to be overwriting memory you don't own.

If there are similar mistakes in your other functions, then I'd say that your memory overwrites are trashing the stack, giving you the bogus error messages.

Best to post a small and complete program which still demonstrates the problem.