I had the same problem and submitted a ticket... They are going to address this issue in a future patch but this is the reply I got.
First, try right-clicking on the event and selecting “Report Player.” If this works, you are done! However, if you are met with the error “Internal Calendar Error,” you can remove the invites using the script below:
1.) Make a new macro by selecting the macro option from the game menu or typing /macro and hitting "Enter".
2.) Copy and paste the following code into the macro window:
/run for i=0,99 do for y=1,31 do t,_,_,_,_,_,_,_,_,iB =CalendarGetDayEvent(i,y,1) if iB=="" or t=="TITLE" then CalendarContextInviteRemove(i,y,1) end end end
*Important: Replace TITLE in the script above, with the name of the spam event*
3.) Place the Macro on your action bar, and click the Macro. Each click will remove only ONE calendar invite.
4.) The invites should be removed at this point.
If you have any additional concerns, please open up a new support ticket and we'll do our best to assist as quickly as possible. Until then, I wish the best of luck in everything you do!
Game Master Velocytori
I hope this helps