Can’t access wordpress dashboard after activating Cloudflare FlexiSSL plugin

I just set up free cloudflare SSL on one of my domains.. another domain under same hosting account is working fine with cloudflare flexi SSL, and I can login to my dashboard too. but after installing flexi SSL and actvating cloudflare flexible ssl plugin to the main domain I cant access my wordpress dashboard for that site..I had to deactivate the plugin from my cpanel.. how to solve that, how can I enable flexi SSL plugin?