wp-content/plugins/events-manager/em-posts.php on line 250

Have you tried:

– deactivating other plugins to see if this resolves the problem. If this works, re-activate the plugins one by one until you find the problematic plugin(s).

– switching to the Twenty Eleven theme to rule out any theme-specific problems.

and check the EM-Plugin-Settings/Pages/Permalink-Slugs. The fields must be filled in.

what’s the whole error text you see?

Warning: strstr() [function.strstr]: Empty delimiter in /**/**/**/**/**/**/wp-content/plugins/events-manager/em-posts.php on line 250

in that case yes you need to set something into your slug values, blank values won’t work (something we’ll prevent being possible when time permits)