Theme installed but demo content import doesn't work.

I have a new site setup and I imported some pages from the old site (built on a different theme).

I then installed the Basel theme and wanted to set up the Demo content – the Lingerie base, but even though it says it was successfully done, the pages don’t appear on my PAGES section of WP. Even if I add them separately as “Additional pages” in the Basel setup.

Is this because I already had old pages in there? IF I delete the old pages (all of them), but not empty the entire WP, will it work then?

Thanks,

ELina