Upon opening the calendar on Saturday, January 1, 2011, an error message indicates that ACT! encountered an error and must be shut down. This is the same problem experienced in the past when the first of the month occurs on a Saturday under prior versions of ACT! and Windows. After shutting down ACT! and changing the system date to Sunday, January 2, 2011, the calendar opens without a problem. Hopefully, this bug will get fixed sometime in the near future.