Mail Merge MS Word with Excel data

I created an MS Word reminder postcard setup to access Mail Merge info in an Excel spreadsheet, including the day of the week and date (e.g. cell format - Sunday, July 27,2008) of each appointment. The only problem is that when it prints in the postcard, it runs the day of the week ahead - prints Monday, July 27, 2008, which doesn't exist! Any clues??