Microsoft made a new patch (KB 2661254) available through Windows Update. This patch has the consequence that the Internet Explorer does not accept certificates which are less than 1024-bit encryption. The Grid Control 11G uses a 512Bit certificate, which means that users get the security warning from IE for EM login, but are unable to login into the Enterprise Manager.
Solution is to create a new certificate for EM. Login into the Server and start following emctl command.
>emctl secure console -self_signed -key_strength 2048 Oracle Enterprise Manager 11g Release 1 Grid Control Copyright (c) 1996, 2010 Oracle Corporation. All rights reserved. Securing Console... Started. Securing Console... Successful
If you access the Oracle Weblogic Server over HTTP then this Problem can also occur. The solution is the same as in the Enterprise Manager => recreate the certificate.
EM Grid Control 11g Console Not Accessible Via Internet Explorer After Applying Microsoft Security Patches On Client PC [ID 1489557.1]
Log in to Enterprise Manager Console using Internet Explorer 7 and higher fails with „Internet Explorer cannot display this page“ or with Security Certificate Error MOS ID 1498203.1
Feedback and comments are always welcome