I use an excel file with suffix is ".xlsx", qaf use CSVUtil to analyze this file, and throwing exception. If I use ".xls" file, it worked well.
As of qaf version 2.1.15 Excel file with xlsx extension is not supported. It is lower priority feature may be because people prefers xml/json/csv format over xls and feature available to have custom data providers as well.
Another alternate is using CSV files (with .csv extension) which can be opened in Excel for editing as well as can be edit/view outside Excel. For example consider git as repository, one can review/edit pull request if it is csv but not if it is xlsx.