Can't get filemtime for .xls file types.

[Anon]

Using the following code I can't seem to get at the last modifed date for an Excel file I have stored in a docs directory. The same code works perfectly on all the other files stored in the same directory. Any suggestions would be most appreciated.

$file = "spreadsheet.xls";

$filemod = date("m/d/y g:i:s A", filemtime("$file"));