I am using Oracle RAC 10g, with Database in 10.2.0.5 version. On Linux 2.6.18-92.1.13.el5 #1 SMP Thu Sep 4 03:51:21 EDT 2008 x86_64 x86_64 x86_64 GNU/Linux .
I have a problem regarding OEM:
Last night we joined in the summer-time, and today we saw that the OEM was not working for one node only . Fine, we did some configuration regarding the Timezone [TZ], checked the OS Timezone, and changed the timezone from the database to -2 [just like the OS].
Ok, we saw that the time worked perfectly, and that node  was working normally, but the other 2 nodes do not show activity, no graphics.
Then i checked the dbconsole:
[oracle@fastora1:/home/oracle]$ emctl status dbconsole
Oracle Enterprise Manager 10g Database Control Release 10.2.0.5.0
Copyright (c) 1996, 2010 Oracle Corporation. All rights reserved.
Oracle Enterprise Manager 10g is running.
Logs are generated in directory /u01/app/oracle/product/10.2/db_1/fastora1_cms1/sysman/log
And then i checked the logs:
The most interesting one is emagent.trc that everytime i try to see the graphics at node1 shows this:
2012-10-22 17:02:27 Thread-4095720336 ERROR fetchlets.oslinetok: Process stderr = ORA-01017: invalid username/password; logon denied (DBD ERROR: OCISessionBegin)
I'm disappointed at the lack of help you're receiving but I think many of us are focused on the Grid Control and Cloud Control environments -- I know that I remember very little about DBControl monitoring. You may get better help here if you can migrate to EM12cR2.
My only suggestion for you is to re-confirm that the password files on each instance are all set up correctly. Take a look at notes 790214.1 and 778805.1, compare the contents of $ORACLE_HOME/dbs/orapw[SID] on each host to make sure they match. Make sure you can login directly to each instance using the passwords you believe are configured for DBSNMP, SYSMAN, and SYS as SYSDBA; use EZconnect strings to reach each instance directly or add new tnsnames.ora entries if needed.
What is the monitoring user - dbsnmp or a sysdba user? Go to Monitoring Configuration page and click on Test Connection. Is that successful? Also, try Test Connection against each RAC instance in the instances table at the bottom of the page. Let me know the results of this first and then we can look at next steps.