Hello,
The down arrow indicates a client deployment, the red X indicates an error.
If you double click the client, you should be able to see the "Deployment Message" towards the bottom of the properties pane, that should tell you the issue.
Check these Threads:
https://www-secure.symantec.com/connect/forums/sep-121-client-status-icon
https://www-secure.symantec.com/connect/forums/definition-icon-sepm-client-list
Secondly, In reference to the "Error 1920 (SepMasterService) failed to start", check these Articles:
SEP installation issue Error 1920 (SepMasterService) failed to start
http://www.symantec.com/docs/TECH187151
When upgrading the SEPM from version 12.1 to version 12.1 RU1, the following error appears "Error 1920. Service W3SVC (W3SVC) failed to start.
http://www.symantec.com/docs/TECH175156
and
Check these Threads with similar issue -
https://www-secure.symantec.com/connect/forums/symantec-installation-error-1920
https://www-secure.symantec.com/connect/forums/error-1920-0
https://www-secure.symantec.com/connect/forums/sep-client-installation-error-message
Hope that helps!!