I lose connection with network whenever put MacBook Pro to sleep or reboot. Lost network configuration. Have to use diagnostics to relocate and reconnect. What is the fix?

Question

I lose connection with network (router: Airport Extreme, latest firmware) whenever MacBook Pro put to sleep. Have to use diagnostics to reconnect. Tells me network configurations have changed, then reconnects me to network. What is the fix?

Answer 1

Try the following, in order, until (hopefully) resolved:
1a. Delete Preferred Network(s)
System Preferences > Network > AirPort > Advanced > AirPort tab
Under "Preferred Networks," delete the network(s) you regularly use from the list.
1b. Delete AirPort Keychain Entries
Launch the "Keychain Access" application located in Applications/Utilties.
Click on the "Kind" filter at the top, and look for any "AirPort network password" entries...and delete them.
1c. Add Preferred Network(s)
System Preferences > Network > AirPort > Advanced > AirPort tab
Add the preferred network(s) using the "+" button.
Restart or log out then back in.
2. Move System Configuration Files
(Note: You will have to reestablish your network connections settings.)
Go to /Library/Preferences
Move the SystemConfiguration folder to the desktop.
Restart your Mac. (Note: OS X will rebuild the files that are now sitting on your desktop. If this doesn't resolve the issue, you can move the folder back to it's original location.)