Let us understand it. Windows is stupid and idiotic system. Suppose, you store (remember) your NAS's Samba username and password, so you don't have to provide it, each time you access your local network share. If you thenchange your user password, Windows either won't detect the fact that password has changed or, even if it detect it, it won't show you login/password dialog box to provide new one. Instead, it continue to provide NAS with wrong (outdated) password.
If you had setup some fail-login restrictions (like I do), that for example blocks particullar IP address after repeated unsuccessfull login, you may end up with blocked access to your NAS from your local network computers. This can happen only on Windows. Let's wave and clap our hands again for Microsoft engineers introducing new understanding of network security!
But, seriously, how to workaround this problem? Go to "Control Panel > User Accounts" and click on "Manage your credentials", which will bring you to "Store credentials for automatic logon" page. Here, locate your NAS address in "Windows Credentials" or "Generic Credentials", click it to unfold and make use of either "Edit" or "Remove from vault" links. In second choice, you'll have to access your network share again and use login dialog that should popup, to provide new password. In first choice, this (password change) should be done directly. But, hey, it's Windows. Nothing is sure here (except that it will eventually crash your hard drive and make you lose everything! :]).
Second of all -- you'll need any way to access NAS outside your local network or from another computer in this network, that hasn't been blocked (yet). Use remote access, GPRS or anything. Fire web panel, login as admin, and go to "System Administration > Security". Locate your local IP address on list on "Security Level" tab, select it and click minus button to remove. Clicking on "Apply" should not be required.
Make sure that you do this via different access provider, as you probably can't access web panel from your blocked computer. And, what is more importat, make sure that you do this AFTER your purge your password vauld from wrong (outdated) passoword or change it to current one. Windows is so stupid, that it uses Samba even in background, even if you don't open any network share. So it get your computer immediately to be blocked again, if you try to unblock it without changing password settings in password vault.