More than likely you have some other file where the setting is manual.
If you open that file first and then open your book in the same session the
latest file will also adopt and retain the manual calc option.
Best solution?
Make sure that all your files are set to have automatic calc option.
if this is impossible you need to set the calc option each time you open
this file via a macro.

--
Greetings from New Zealand

"Renny Bosch" wrote in message
...
Occasionally when I open an Excel file and enter some data I discover that
the option to automatically recalculate all formulas has been cleared. I
am
talking about Excel Options | Formulas | Calculation Options | Workbook
Calculation | Automatic. Windows XP, SP 3, Excel 2007, SP1 MSO. I do use
a Personal.XLSB file.

The file to which this happens contains a very large number of formulas,
including conditional formatting. Does that have anything to do with it?