Question on volatile keyword

I was wondering why I would receive this error when I add the volatile keyword - I am new to embedded C but my understanding was that it just told the complier not to optimize the variable?

This code give me no errors

void display_text(char *dispString)
{

   char myLcdBuffer[20];
   U32 i;

   my_strcpy(myLcdBuffer, dispString);

   /*
    * Send the data to the LCD screen
    */
   for (i = 0; i < strlen(myLcdBuffer); i++)
  {
     SER_PutCharLcd(myLcdBuffer[i]);
  }

}

However if I add the volatile keyword to the char myLcdBuffer

void display_text(char *dispString)
{

   volatile char myLcdBuffer[20];
   U32 i;

   my_strcpy(myLcdBuffer, dispString);

   /*
    * Send the data to the LCD screen
    */
   for (i = 0; i < strlen(myLcdBuffer); i++)
  {
     SER_PutCharLcd(myLcdBuffer[i]);
  }

}

I get this error msg - error: #167: argument of type "volatile char *" is incompatible with parameter of type "const char *"