Redmine

I am not able to see the "Administration->Settings->Authentication" tab.
When I open this tab, it displays nothing.
It did not give any error also. I tried reinstalling the plugins and clearing the cache. But no luck.

can anyone help me on how to resolve this ?

My redmine info is as below
Environment:
Redmine version 2.5.1.stable
Ruby version 1.9.2-p320 (2012-04-20) [x86_64-linux]
Rails version 3.2.17
Environment production
Database adapter Mysql2
SCM:
Cvs 1.12.12
Filesystem
Redmine plugins:
redmine_auto_watchers_from_groups 0.0.2
redmine_banner 0.0.8
redmine_graphs 0.1.0
redmine_logs 0.0.5
redmine_maintenance_mode 1.1.0
redmine_reminder 0.3.1