Plesk: WP in https, archives are 404 in http

I’m setting up WP for a client. She wants WP to run under https and the blog pages (including archive pages) to run under http. Her account has Plesk and LAMP. I’ve installed WP 2.1.3.

On the Options > General page in WP, the WP URL is defined with https, the Blog URL is http. However, when I click an archive link on the main blog page, it comes up with a 404. When I add an s to the URL (e.g. https), the page comes up fine.

I set permalinks on the Options > Permalinks page which appeared to write to the .htaccess file on the httpsdocs side of Plesk but not the httpdocs side. The file size of the .htaccess file in the httpsdocs folder appears to increase in size (from 0 to 214). However, copying it to my computer from the server shows a blank page.

Any ideas how to get the archive pages to display under http (that is, using the httpdocs folder in Plesk)? Has anyone encountered this problem before? Thank you!

Tim