Easy solution

After you changed your password, when you are logging in ECCS's Mac environment,  a window about Keychain will appear. On this window, you choose "Create new keychain" and you can fix completely, but you lose your passwords stored in Mac environment. However, if you choose "Update Keychain password" and input your previous password, you can use your passwords stored as well as you used before.

refer to：https://www.ecc.u-tokyo.ac.jp/announcement/2010/04/09_1301.html (Japanese only)

What's the Keychain?

Refer to HWB (only in Japanese)

When it happens

When you are required to unlock your login keychain, please input your previous password. After that, open keychain access via the key mark button on the right top menu bar. And then, "Edit" -> "Change Password for Keychain "login"...". Then, input the previous password and a new password.

However, if you forgot your previous password, you cannot fix your keychain. Please refer to キーチェーン “ローカル項目” のロック解除を要求される.

「"Messages Agent" がキーチェーン "ローカル項目" を使おうとしています。」などと表示された場合

キーチェーン "ローカル項目" はログインキーチェーンのように削除できないので、個別の対応が必要となります。こちらの場合もやはり、キーチェーン “ローカル項目” のロック解除を要求されるをご覧ください。