Hi,
Sorry for delay, just back from travel.
It's amazing what you told me, I'll inform the author about this conversation in order for him to fix it. I already see that, Wordpress is a little bit permissive with license because, I guess, they don't have time to check that.
I've done the modification but still got the same bug with 404 pages.
Should I install wordpress version full GPL like he told?
http://wordpress.org/extend/plugins/all-in-one-event-calendar/
Thanks !