I wrote earlier:
Try altering Access field's format to "General Date" or using DateTime.Today instead of DateTime.Now as value to be updated.
In Ron's case the Date/Time field is used in SELECT clause's WHERE criteria, but I think the solutions works with it too. Furthermore this error is not caused by iBATIS. I believe MS Access is to blame for this issue.
Regards, Jarmo
P.S. Thousands thanks for the developers and contributors of iBATIS.NET. I'm quite new to iBATIS, but I am already falling in love with it :-)