From Mac Help for Keychain:
Solving problems with keychains
If you have some experience administering computers, you may be able to identify and resolve some keychain problems by using Keychain First Aid.
With Keychain First Aid, you can:
Verify and repair keychain settings and permissions
Reset a keychain (delete a keychain reference while preserving the keychain file)
Make the login keychain password the same as the login password
Set the login keychain as the default keychain
Set the login keychain to always remain unlocked
To use Keychain First Aid:
Open Keychain Access, then choose Keychain Access > Keychain First Aid.
Enter your user name and password.
Select, Verify and click Start. Any problems found will be displayed.
If there are problems, select Repair and then click Start.
To change the Keychain First Aid settings, choose Keychain Access > Preferences, then click First Aid.
My emphasis - it is important to check the prefs before using First Aid to make sure they will do what you want them to do.