Permalinks breaking title tags (“Page not found” title tag error)

I tried to figure this out, and I Googled anything I thought was remotely similar to this problem.

Basically, I am developing a WordPress based site for a client when I ran into this problem that has me completely miffed.

The problem is this: I installed a few plugins (the last one I believe was sitemap-generator (basically generates a php sitemap that you can include into a custom template page) — this one, https://www.dagondesign.com/articles/sitemap-generator-plugin-for-wordpress/

I noticed that after I installed it, some pages that I generated from the admin (regular content pages) are generating bad title tags. For example, the /sitemap/ pages title tag reads “Page not found – [SITE TITLE], as does the /media/ (both of which I created after installing the plugin listed above). Now I have since removed the plugin, and subsequent pages generate fine. /sitemap-2/ reads “Sitemap – [SITE TITLE],” as it should. However, even if I delete the old /sitemap/ page, and create a new one, it will still break the title tag.

More problematic, if I change the permalink structure to the original ugly structure ?p=1, all of the title tags (including those previously broken) resolve themselves.

I have absolutely no idea how or why this is happening, and I would very much appreciate solving this issue! Thanks in advance!

Details:

I have setup the permalink structure as follows: /%postname%/

My title tag is as follows: <?php wp_title(‘-‘, true, ‘right’); ?><?php bloginfo(‘name’); ?>

My .htaccess file has not been changed (although I noticed it appeared to have been re-written at about the same time that I noticed the title tag error). However, it is the same as a default .htaccess file.

The site is self-hosted.

Please if anyone can help me out here, I would really appreciate it! Thanks!