Users can't login into their dashboard

I've created a new mu site and created test users for the name.domain.com

When I tried to login into the user's admin dashboard, I was presented with the easy blogging interface option but before I could make a selection the page started refreshing or redirecting and never actually load.

I have tried renaming the mu-plugin directory and the problem actually stopped and I know that it's one of the plugins in the mu-directory that is causing the problem.

How do I find out which plugin that is causing the problem? I've tried deactivating plugins by deleting the files but I got the error saying failed to open stream: no such file or directory for the deleted plugin instead.