VERY Weird Date Format Problem with Macro

I'm using a macro to copy data from one worksheet to another. It has always worked perfectly until today. For some reason the date in the destination workbook is 1 day and 4 years behind the original.

It's automatically doing something like this =DATE(YEAR(C2)-4,MONTH(C2),DAY(C2)-1)

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I've tested different workbooks, and different dates, as well as different date formats. I've even tried it on two different computers. I cannot figure this out. Any ideas?

MrShorty, that's exactly what it was. I had never even heard of the 1904 vs 1900 date issue.

Thanks so much for your help!!