I have found that Monarch likes to append to a table already made by Monarch. You need to make the initial table from a Monarch export and then it should accept future appends OK. If necessary export a table then append the Excel bit to it and see if that works.
The problem is more than likely with Excel and its Date/Time formats being more than you can see on the screen.
Thanks for that, as I have a lot of old information in the excel spreadsheet that is cleared out monthly from my source report i could not export the initial table.
However, i exported the current info into a seperate tab and copied the column i needed, then copied the dates i needed and deleted the offending column.
Fingers crossed that seems to be working for me!