login error message

probably a plugin is throwing this warning.

To find out, try deactivating ALL plugins temporarily to see if this resolves the problem. If this works, re-activate them individually (one-by-one) to find the problematic plugin(s). When you can’t get into your admin dashboard, try deactivating via FTP or SFTP or whatever file management application your host provides (also read http://codex.ww.wp.xz.cn/FAQ_Troubleshooting#How_to_deactivate_all_plugins_when_not_able_to_access_the_administrative_menus.3F). Also remember to deactivate any plugins in the mu-plugins folder. The easiest way is to rename that folder to mu-plugins-old.