Not able to register or Login

I’ve installed WordPress Multisite. I’ve four blogs.
http://newsbird.in
http://technology.newsbird.in
http://business.newsbird.in
http://jobs.newsbird.in

I’ve problem login to or register to the http://jobs.newsbird.in site through the url http://jobs.newsbird.in/wp-login.php OR http://jobs.newsbird.in/wp-admin/

When I click on these links it’s automatically redirecting to http://jobs.newsbird.in

While I dont have any issues with other 3 blogs, only the jobs website have this issue.

I guess it’s the problem with some plugin. till recently it was working fine. after installing some plugins I’m not able to login & finding it hard to find which plugin causing this isuue.