iCloud calendar shows constant pop up error about bad URL 404
Someone please help me with this. Its been going on for months and I'm at my wits end. I cant use my calendar on my Mac at all without a constant pop up every few seconds telling me my iCloud calendar server responded with a 404 error. I updated to El Capitan when it first came out but only had this issue starting about 3 months ago. How do I fix this??
MacBook Pro (Retina, 15-inch, Mid 2014), OS X Yosemite (10.10.3), null