Are the years in your dates being written to the database as YYYY, ie the full 4 digit year num? I recall MS changed the way Access interpreted dates to try and combat the so called Y2K problem. I can't remember the cutoffs, but it was something like, eg if 31/1/29 was entered it would be assumed to be 31/1/2029, however if 31/1/30 was entered it would be treated as 31/1/1930.

Also the fact that this happened when it reached a February date may provide a clue, given that February has 29 days in a leap year. Perhaps there's some screwed up data in the database.

Just a thought...