PenciDesign replied
Hi,
It seems you didn't read the "NOTE IMPORTANT" on the import demo data page ( Appearance > Install Plugins ). After import a new demo, you should uninstall old demo.
For now, if your site is new site, no old posts, pages to keep - you can use plugin WP Reset to reset everything to default like when you just install WordPress and do the import again.
Best Regards,
PenciDesign