Why am frequently asked for access to my Keychain?
The Local Items keychain was introduced on Mavericks and holds iCloud keys for offline use.

However, sometimes OS X will repeatedly ask you for the password. This can be solved by deleting the folder named with an UUID like A8F5E7B8-CEC1-4479-A7DF-F23CB076C8B8 from ~/Library/Keychains/ and then reboot. No keys will be lost in this process.

This is described here: http://support.apple.com/kb/TS5362