If you have changed your IT password, the Keychain on the Mac detects that the password is different when you login.
If you can remember your old password, choose Update Keychain password. You will then need to enter your old password one last time in the pop-up window that appears. Any stored passwords or data for websites or applications will then be kept in your keychain.
If you can't remember your old password, click on Create New Keychain. Enter your new IT password when prompted.
There is a third option called Continue log in. It's fine to click on this button, it just means you will keep getting the warning message until you choose one of the other options.