For those that are NOT tech savvy, contact your hosting company and let them know that you are getting a 310 error "too many redirects", let them know what version of WP you have and also let them know that you updated the Impact plugin and are pretty sure that is the issue. They will deactivate the plugin and you will have access again to your admin. (they may need your user and pass for your wp admin to do this. I know that my hosting service needed it)
For those that are familiar with your FTP, just go into the plugins folder of your WP content, find the impact folder and either rename it or delete it all together.
Beyond this, if you want to keep the plugin, reinstall the older version and DO NOT UPDATE until the developer fixes the issue.
Hope this helps. I am not marking this resolved as the problem is not resolved at all. this is just a fix to get back into your admin.