I am no longer able to import data from a spreadsheet into Mathematica. A long time ago I used to do this from Microsoft Excel, but now I have Libre Office. I can still import files that I at the time made with Excel, but Libre Office calc files are not accepted, no matter whether I save them in Libre Office as .xls, .ods, or xlsx-files. Except for files that I in the old times made with Microsoft Excel, a command like list=Import["D:\Data for Mathematica\xls-files\test.xls"] no longer works. Each time I get the message "file not found during import". What am I doing wrong?