This has xl97 in the subject, but maybe it applies:

http://support.microsoft.com/default...b;en-us;196620
XL97: "Cannot Empty the Clipboard" Error Message When Dragging Cells

Tore K. wrote:

I always get a "Cannot empty the clipboard" pop up warning when doing a
drag'n'drop in Excel. This version is part of Office 2003. This never used to
happen in Office 2000. I have not been able to fine a place to turn this off.

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Dave Peterson