I had the same problem and I came to the conclusion that the problem was not a conflict with another plugin but the PHP memory limit. Most likely when you disabled the All in One Event Calendar your freed up enough memory to load the SEO plugin properly but you would get the same by disabling one or more other plugins (All in One Event Calendar is a bit heavy on PHP so you might have to disable more than 1 plugin to get the same result).
To solve the problem increase PHP memory limit in php.ini:
memory_limit = 256M;
If you do not have permissions to change the settings in php.ini contact your hosting company and ask them to do so.
Hope that helps.
