Q: the wifi could not be joined
when i try to join my home wifi it connect but after sbout 2-3 hours the internet stop and when i try to connect again it show the message in the photo
and doesn't connect and the wifi works perfect on other devices i teried every thing including changing the router it self 
MacBook Pro with Retina display, OS X El Capitan (10.11.3)
Posted on Jan 22, 2016 9:36 AM
Another thing to try...
Go to System Preferences
Click Network
Highlight AirPort and click Configure, (might be Advanced in later OS versions)...
Choose “By default, join: Preferred networks”
Select your access point and Remove your access point with the minus button.
Launch your keychain access in Utilities and delete your access point keychain entry, looks for duplicates.
Reboot
Go back to the “By default, join:” page and click the plus this time to add your access point. Enter the correct password, save, reboot.
Posted on Jan 23, 2016 10:25 AM