Multitimeframe EA (consult and advise needed) regarding handling 4066/4073 errors and how to find them.

Request for consultant / advise on the following:

Subject:
How to handle 4066/4073 before accessing candle/indicator values.

Background information:
For example: an EA that uses MACD on 5M and MACD on H4 (how to handle 4066/4073 error before accessing candle/indicator values)  

I'm told in the forums that I have to call the function provided (with H4) at the beginning of start and if it returns false, I return and wait for a new tick

The Project Details:

1. Explain the process of handling 4066/4073 error before accessing candle/indicator values.
2. Show/Explain to me where the 4066/4073 errors might occurs in the code process and why.
   
3. Clarify what this statement means exactly "call the function at the beginning of start".  Whether that be OnTick() or OnInit() or what this statement refers to