OS X 10.8.4 wifi says "connection failed", but connects anyway; cannot save password

Question

I am using OS X 10.8.4 that came with my MBP. When I connect to my home wifi that requires a WPA 2 password, it says "Connection Failed", but anyway connects to the internet. Also, my password is not being saved, and I need to enter it everytime.
After reading several forums, I have already tried the following:
1. removing airport preference list from Library/Preferences/SystemConfiguration
2. Removing network password from the keychain
3. Using Keychain first aid
4. Using disk utility and doing repair disk.
5. Doing DHCP release in Network Preferences.
6. Removing my network from the preferred network list and connecting again.
I am using a D-link modem. It should not be a problem, because the same MBP could remember the password before. The problem happened when I tried to fix my wifi because it would take long to connect after waking from sleep, when I deleted the airport preferences list, and removed the keyring.

Answer 1

Back up all data. Don't continue unless you're sure you can restore from a backup, even if you're unable to log in.
This procedure will unlock all your user files (not system files) and reset their ownership and access-control lists to the default. If you've set special values for those attributes on any of your files, they will be reverted. In that case, either stop here, or be prepared to recreate the settings if necessary. Do so only after verifying that those settings didn't cause the problem. If none of this is meaningful to you, you don't need to worry about it.
Step 1
If you have more than one user account, and the one in question is not an administrator account, then temporarily promote it to administrator status in the Users & Groups preference pane. To do that, unlock the preference pane using the credentials of an administrator, check the box marked Allow user to administer this computer, then reboot. You can demote the problem account back to standard status when this step has been completed.
Enter the following command in the Terminal window in the same way as before (triple-click, copy, and paste):
{ sudo chflags -R nouchg,nouappnd ~ $TMPDIR.. ; sudo chown -R $UID:staff ~ $_ ; sudo chmod -R u+rwX ~ $_ ; chmod -R -N ~ $_ ; } 2> /dev/null
This time you'll be prompted for your login password, which won't be displayed when you type it. You may get a one-time warning to be careful. If you don’t have a login password, you’ll need to set one before you can run the command. If you see a message that your username "is not in the sudoers file," then you're not logged in as an administrator.
The command will take a noticeable amount of time to run. Wait for a new line ending in a dollar sign (“$”) to appear, then quit Terminal.
Step 2 (optional)
Take this step only if you have trouble with Step 1 or if it doesn't solve the problem.
Boot into Recovery. When the OS X Utilities screen appears, select
Utilities ▹ Terminal
from the menu bar. A Terminal window will open.
In the Terminal window, type this:
res
Press the tab key. The partial command you typed will automatically be completed to this:
resetpassword
Press return. A Reset Password window will open. You’re not  going to reset a password.
Select your boot volume ("Macintosh HD," unless you gave it a different name) if not already selected.
Select your username from the menu labeled Select the user account if not already selected.
Under Reset Home Directory Permissions and ACLs, click the Reset button.
Select
 ▹ Restart
from the menu bar.