Hello claghorn,
Sorry for the redirect issues you are having with the redirects. We can help you out here.
First are you able to delete the plugin using ftp or through your cpanel to get the login working again?
Also are you using Multisite with the plugins.
Let us know about those two and we can go from there.
Also when you come back to us with more information can you please create a new ticket as we are able to better help you on your own ticket and jholliday gets emailed every time we post here and I am sure jholliday would prefer not to have that happen.
So I am closing out this ticket, but claghorn please let us know so we can help you out and get this resolved.