I found this very useful link while i was facing a lot of errors regarding JCO connection :
This link also solves the part of :
Check if the ECC system exists and the Technical system is configured properly.
Every time i need to start the Java Visual Administrator , i spend huge time just searching for the directory , and as i m not a basis consultant , i tried to search SAP Library for solution to my problem .
Also i decided to write the directory in order not to forget anymore 🙂 .
Hope this help anyone facing the same problem Insha’allah .