Assume that you open multiple workbooks at the same time in Microsoft Office Excel 2007 on a computer that is running Windows 7. Then, you point to the Excel taskbar button. However, the taskbar thumbnail preview feature in Windows 7 displays Excel icons over a gray background instead of previews of the workbooks.
To work around this issue, enable the Show all windows in the taskbar option in Office Excel 2007. To do this, follow these steps:
In Office Excel 2007, click the Microsoft Office Button, and then click Options.
Click the Advanced category, click Display, and then select the Show all windows in the Taskbar check box.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.