Unable to import Theme Unit Test content

I have a wordpress installation I plan to use for theme development (having moved from using other web dev tools to wordpress) but the Tools>Import function will not work, simply saying “an error occured” (not exactly helpful). I’ve tried changing the permissions on the wp-content directory and it’s sub-directories. Can anyone point me in the right direction please? The installation is at https://unlimitedmarketing.net/wordpress/

Thanks in advance

frank