Solution 1: The easiest solution is to clear the cache, try to login from a different browser or incognito/private browser mode.
Solution 2: If the first solution doesn't work, it is necessary to deactivate the 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 “patchstack” folder into “webarx1”;
After you log into your dashboard, you can rename the folder back from "webarx1" to "patchstack" and disable reCaptcha from Patchstack plugin settings.