Solution 1: The easiest solution is to clear the cache, try to login from different browser or incognito/private browser mode.
Solution 2: If first solution doesn't work, it is necessary to deactivate plugin manually. Please complete the following steps:
- Go to the /wp-content/plugins folder via FTP (http://codex.wordpress.org/FTP_Clients);
- Find and rename “webarx” folder into “webarx1”;
- After you log into your dashboard, you can rename the folder back from "webarx1" to "webarx" and disable reCaptcha from WebARX plugin settings.