Excel : The name that you entered is not valid.

When I try to use NumXL functions in a worksheet with a live DDE/DDX links, but Excel pops up an error message dialog

The name you entered is not valid"

Reasons for this can include:
-The name does not begin with a letter or an underscore.
-The name contains a space or other invalid characters.
-The name conflicts with an Excel built-in name or the name of another object in the workbook.

Note: This happens even if I don't select/use the live cells range in my NumXL functions. To work around it, I copy the desired data, paste it by value to a separate sheet, before I can use it with NumXL.