I've been trying to join tables to a shapefile. In the past this has worked by converting a .csv file to and excel file. However, with version 10.4 I have only been able to add tables into ArcMap if they are in .xls (Excel 97-2003) format. If I try to bring a table in in .xlsx (Excel 2016) format, I get the error "Failed to connect to database. Class not registered." Is this change due to different versions (I'm using 10.4)? Everything seems to be working fine when I convert to .xls, but I would prefer to use .xlsx since it is the most recent version. Is there any way to do this? I was also wondering if there might be future problems with using the 97-2003 excel format?