Error Indication & connection failure

[guess.who]

Dear members
I am really confused between the causes of Error indication and connection failure.. some say error indication is due to faulty hardware , some say due to transmission issue and others say it is coz of interference or coverage issue.... Please tell me which one is correct... and answer only if you are 100 % sure.... i dont wanna get more confused ...i hope no one gets offeded by my request and understand it....Thanks in advance BR
GW