InStat gives the incorrect message "This file is not an InStat data file"

 GraphPad InStat 3.1 allows more columns (52 vs. 26) and more rows (10,000 vs. 1,000) than earlier versions of InStat. If you save a file with more  than 1000 rows or 26 columns, older versions of InStat will give the message "This file is not an InStat data file". That is not 100% true. The file IS an InStat file, but it cannot be opened by prior versions of InStat. Note that the update from InStat 3.0 to 3.1 is free.