Cannot login Enterprise Manager

It happened to me the other day: I could no longer login to an Enterprise Manager site, and I was sure I had the correct password. It might have something to do with running ssoReplSetup.jar.
Anyway, the solution is to use a hidden option of emctl: reset. These are the steps to revitalize your OEM:

1. edit $ORACLE_HOME/sysman/j2ee/jazn-data.xml
2. find ias_admin entry
3. remove line with "credentials"
4. save file
5. emctl set password reset <new_password>
6. (re)start oem: emctl start iasconsole

You can now login again, using <new_password>.