This error is due to a setting within Excel and not with Sphere itself.  To resolve:

Excel 2007
1. Click the Office button in the top left
2. Click Excel Options
3. Click Advanced on the left side of the window
4. Scroll down to the section labeled "General"
5. Remove the checkbox next to "Ignore other applications that use Dynamic Data Exchange (DDE)"
6. Click OK
7. Attempt to export again

Excel 2010 and 2013
1. Click the File tab
2. Click Options
3. Click Advanced on the left side of the window
4. Scroll down to the section labeled "General"
5. Remove the checkbox next to "Ignore other applications that use Dynamic Data Exchange (DDE)"
6. Click OK
7. Attempt to export again