Shane, is the client connecting to Outlook 2013 via ActiveSync or Add to Outlook? Also, are you running the latest version of SM? If your client is using EAS, and he is willing, see if he is willing to remove the account from Outlook then re-add it. If not, you may want to open a support ticket so that we can look at this actual calendar file. If it is determined to be a bug, your ticket would be refunded.