Thank you for reaching out to the Community! I do apologize, but when trying to export a custom report some customers are reporting that they are receiving that same error. This is a defect that we are aware of, and the work around is to export a full report instead. I apologize for any inconvenience this may have caused, and I hope you have a wonderful rest of your Sunday!
I apologize we do not currently have a time estimate of when this error message will be resolved. At this time we are only fixing critical issues on our events program. Though we are not planning any further development at this time, I have tracked your experience in the event that there is any change in the future. In the meantime, did exporting the full event report help you get a copy of the details you needed?