Does this happen when you try it on the practice file on the demo page?
If the practice file works fine, then please send us your file and I will take a look. Otherwise, there might be a problem with some modules of your Excel. You can try go to Control Panel->Microsoft Office->Support information link there you will find a button to "Repair". Do that and usually it fixes this type of VB error.
I've been getting the same error ever since upgrading to Excel 2007. I even reformatted my computer, reinstalled 2007 and then reinstalled DigDB. No luck.