Upgrade from 32-bit ubuntu 6.0x to 64-bit ubuntu 8.04 (Zimbra v5.0.16)
Network Edition: Moving from 32-bit to 64-bit Server - Zimbra :: Wiki

The ldap password instructions do not seem to be complete (step 3). After migrating I got the same error as this thread: [SOLVED] Postfix: Unable to Bind: 49 invalid credentials.

My fix (v5.0.16) was similar to that given there (see [SOLVED] Postfix: Unable to Bind: 49 invalid credentials.) but instead of editing the actual ldpa files in /opt/zimbra/conf I replaced ALL instances of the new ldap_root_password with the new one and not just ldap_root_password and zimbra_ldap_password as per these instructions. (I used vi on the localconfig.xml file and did ":% s/64-bit-password/32-bit-password/g" to replace the generated password with the one from the old server). Them zmcontrol stop and zmcontrol start. Then it worked.

I've added these comments to the discussion part of the wiki page.