Why I can't login Tomcat 7 manager?

In Tomcat 7, the password in the setting file:

tomcat-users.xml

is displayed as string encrypted by md5.

In server.xml file:

<Realm className="org.apache.catalina.realm.LockOutRealm">
<Realm className="org.apache.catalina.realm.UserDatabaseRealm" resourceName="UserDatabase" digest="md5"/>
</Realm>

echo -n yourpassword | md5sum

make sure you change the password in tomcat-users.xml with md5 encrypted string.