I fixed it for Flevotrack. Many plugins were not updated for a while, including Events Calender.
I got back in by disabling all plugins by renaming the plugins folder on the server side. After logging in, update the plugin(s) and WordPress. Should help. Good luck.
We have the same problem, but it turns out it is the php version on the server side that is too old to properly run the latest version of MaxButtons. We now asked the host to run a higher php version and we assume the plugin will work again after that has been done.
Hope this info might help you.
I have the exact same problem. I cannot log in or anything. I would like to fix this issue and keep using this plugin.
Anyone?
