Same Problem here. I just tried to see if Jasper might be useful to me, but on my first report i got the same error. I tried to change the data type of the field, but it doesnt work. It also seems that this problem exists with every field from the Excel, as it doesnt work if i just remove the field that had the error. However, i just tried to build a report that based on a .CSV and it did work. Is it possible that Jasper has a Problem with Excel?