I was able to resolve this by resetting the Permalink slugs in the Events Manager settings.
I also have this error. I just updated to the latest version of the plugin, i have the latest version of wordpress, i disabled every other plugin and confirmed it was events manager. Here are the steps to recreate if the error is displayed.
1) Disable Events Manager (error still displayed)
2) Change permalinks from Post Name to Plain
3) Save (error gone)
4) Change permalinks from Plain to Post Name (Error still gone)
5) Enable Events Manager (Error Reappears)
If Events Manager is left enabled and permalinks are switch from Post Name to Plain the error goes away, but if they are set back to Post Name and Events Manager is still enabled the error will persist. Hope this helps, let me know what else i can test.
