help using the flash.h library and functions

I tried this, but it's still not workig:

void sendMessage(String myMessage) {

    i = 0;  //reset display character counter
    LCDclear();
    while(1) {  //loop 
        if(millis() - prevLCDtime > 100 ) {  //continue every 10 ms
            prevLCDtime = millis();        //update the time counter
            Serial.print(myMessage.charAt(i));    //print the next letter to the display
            i = i + 1; //increase counter
            if (i == myMessage.length()) break;  //when the counter i gets to the end of the message, break
        }
    }

The reference page showed the STRING.charAt(), and STRING.length() which seem to be what I need if I pass a STRING to the function, but I get the error:

Coffee_Water_Station_V5_1_2.cpp: In function 'void SaveSettings()':
Eeprom:28: error: conversion from '_FLASH_STRING' to non-scalar type 'String' requested

???
thanks.