A couple things to help troubleshoot the issue;
A screenshot of the error
A screenshot of the application
Your BBSettings file
The application logs (you can find these via the Help menu)
The URL of the blog you are attempting to add
The URL of the blog you are attempting to restore to
The XML file you are attempting to restore to that blog.
If you could zip all this up and email it to me (gduncan411 @ hotmail. com) I'll dig into it and try to see what's going on...