Operation Could Not be Completed on Upgrading iBank 3 to iBank 4

I am running iBank 3 on my Mac and I am upgrading it to iBank 4 when an error pops up. It is saying something about NSXMLDocument. I'm not sure what it means and how to fix this. Can someone please send me step-by-step method on how to fix it? Thanks.

The operation couldn't be completed. *** _ [NSXMLDocument

initWithData:options:error:]: nil argument

OK