Authentication problem means you are either...
1. Connecting to the right WiFi (yours) but inputting the wrong password.
2. Connecting to the wrong WiFi (not yours) but inputting the right password for 'your' WiFi.
3. Connecting to the wrong WiFi (not yours) and inputting the wrong password (even for yours).
So check that it is actually 'your' WiFi you are trying to connect to. Once you are sure that is correct, then I suggest checking the password to make sure you are inputting the right one.