Looks like there was an issue in the plugin with the login page. Should be fixed in 0.7.7. Let me know if it works now.
If count categories > 1000 their loading is very very long in admin panel, more than half a minute, at a sufficiently good server.
Can do pagination with sorting and searching?
Submit an Issue.
Feature Requests can be found here.
@nhl.pl thanks, but I want to still discuss it here
Pagination may be a bad idea because we make the categories sortable on this list.
The underlying code can probably be improved. Please post an issue