Permission problem after import data

Hi!

I’ve just buy the template and installed on a new WordPress 4.0 instance. Everything was fine but after importing the content, WordPress told me that it has to upload the database and after that I can’t access the admin (always shows the error “You don’t have sufficient permissions to access this page”). I tried installing the theme on a WordPress 3.9.1 and the result was the same.

What can I do?

Thanks!
Regards