You are getting this error when trying to import an item since this item already exists in the database, probably it has been added the first time you run the StartUp wizard, just before getting the first error. It's the first error that is the real reason of the problem.
Could you please send us the ~/App_Data/Sitefinity.log
file to see the first logged exception or just post it to this thread.
For the time being, you can clear the checkbox at the third step of the wizard to continue with the project.
the Telerik team