Calendar - Strange iCloud Error Message

HI,

I recently started receiving the following error message upon importing some events for meetups downloaded from the meetup.com website. I never previously had any error messages in the past after importing iCal events into Calendar.

I receive the error code 400 along with a message that says: "The request for "event title" in "calendar" in account iCloud failed. The server responded with 400 to operation CalDAVUploadDropBoxFileQueueableOperating" (attached is a screenshot of the dialogue box displaying this error message).

I seemed to have connectivity issues with iCloud since updating to Yosemite, though the issue here probably has nothing to do with the update.

Can anybody decipher the error message for me?