Log-in stops working

I’ve had this issue twice this week when trying to set up a network using this plug-in. Note: I have 2 networks using this plug-in successfully. However, when I try to set up a new network and follow the recommended steps, the log-in page no longer appears. (server error 500 appears instead). I installed the plug-in, moved sunrise.php to correct location, and added the sunrise line to wp-config. At that point, I no longer have access to the WordPress installation. Very frustrating. Hosting company’s tech support team could not resolve. Please help. I do have access via FTP.

Note I tried deleting the plugin and sunrise file via FTP and adding back the original wp-config file, but that did not fix this issue.