We have one workbook that is automatically formatting every cell on every sheet to date format when the workbook opens.
It is an xlsm. Office 2010. Only this workbook.

If you insert a blank worksheet into this workbook, every cell on the new worksheet is automatically in date format.

We have gone through every sheet (over 20) and corrected the formats correctly several times to no avail.

Every once in a while, only when the workbook is opened - wham - all dates again.

The fact that if you insert a new worksheet into the workbook and all cells are automatically in date format is telling. What could cause the default format of an inserted worksheet to be in date format immediately after insertion.

This problem is only seen in this one particular workbook. MADDENING.

Any thoughts on why a new worksheet in this particular workbook would be in date format instantly. Any ideas as to what can be changed so that a new worksheet defaults to general format as in every other workbook would be greatly appreciated!!!!!!!!!!! I can't help but feel there is an association between the default format of an inserted worksheet being in date format and the problem where all cells in every worksheet change to date format.

As always, any thoughts/help are greatly appreciated.