Well done on the fix. The best and the must to work one !
Were the files originally excel files ? Take ownership of those too.
Now, go to control panel > Folder Options > View tab, and uncheck this option, and see what is the extension name for those files.
If those files are originally excel files, change the extension name to .xls (excel 97-2003 document) or .xlsx (above).
It should work.