To resolve this problem yourself, follow the steps for your version of Microsoft Excel:
Microsoft Excel 2010
Click the File tab, and then click Options.
Click Advanced, and then click to clear the Ignore other applications that use Dynamic Data Exchange (DDE) check box in the General area.
Click OK.
Microsoft Office Excel 2007
Click the Microsoft Office Button, and then click Excel Options.
Click Advanced, and then click to clear the Ignore other applications that use Dynamic Data Exchange (DDE) check box in the General area.
Click OK.
Microsoft Office Excel 2003 or earlier versions of Excel
Click Options, on the Tools menu.
Click the General tab.
Click to clear the Ignore other applications that use Dynamic Data Exchange (DDE) check box, and then click OK.