Login failed to Dell OMSA site on ESXi 5.1

You may receive a Login failed…. error when trying to log into the Dell OpenManage Systems Administrator (OMSA) site on a Dell server running VMware ESXi 5.1 from a Managed Node. The full error is below:

Login failed....
Lockdown mode is enabled in the managed node. For more 
information, see online help.

In this example, Lockdown mode was not enabled, so could not be the cause. I was able to verify this by running the following command while connected to the server via ssh:

[root@esxi1 ~]# vim-cmd -U dcui vimsvc/auth/lockdown_is_enabled
false

From the above you can see that the response was false, meaning that Lockdown mode was not enabled. Once that potential cause has been eliminated, simply restart the Dell OMSA services from the console or via ssh. To do so, run the following command:

[root@esxi1 ~]# /usr/lib/ext/dell/srvadmin/bin/dataeng restart
[root@esxi1 ~]# /etc/init.d/wsman restart

Once the Dell OMSA services have been restarted you should be able to log into the OMSA site and carry out the required tasks.

If you receive a not found error for the /usr/lib/ext/dell/srvadmin/bin/dataeng restart command, per the below:

[root@esxi1 ~]# /usr/lib/ext/dell/srvadmin/bin/dataeng restart
-sh: /usr/lib/ext/dell/srvadmin/bin/dataeng: not found

then try restarting all services by running the command below:

[root@esxi1 ~]#/sbin/services.sh restart

Once all the services have restarted try again and you should be able to log into the OMSA site!

Reference:
Restarting the Management agents on an ESXi or ESX host (1003490)