I am using the sample expense report form provided in Excel 2007. I have a
refund on an expensed item that I need to account for. When I enter a
negative number like -10.23, an error message pops up, "You must enter a
dollar amount in this cell".

No entry style that I have tried will work; not minus or Parens; or typing
in $ symbols. All generate the same error. The cells are aformated by default
as Accounting Numbers, which do not show a negative number format. Changing
the format to Currency, and any style of Negative number does not work
either.

Is my spreadsheet corrupt, or is this a new feature?