"No input file specified." from login page after upgrading to 2.25.7

[krahe]

I recently upgraded to 2.25.7 using Softaculous from an earlier version. I can't remember the version I upgraded from, but it wasn't that old, maybe 2.25.2 or 2.25.3. Anyway, after upgrading, Mantis is broken. Whenever I access the page, "<domain>/mantis/login_page.php", all that comes up is a blank page with the message, "No input file specified." I'm at a loss as to where to go from here. I unfortunately didn't take a backup before applying the update. Any suggestions would be appreciated.

UPDATE:
After backing up version 2.25.7, I restored a backup of version 2.25.2 that I had taken a few months ago. However, I am still getting the same error, so I now suspect the issue is something other than Mantis itself.

[krahe]

My hosting service's technical support found a configuration problem with the .htaccess file on my site, which was causing issues with PHP. They fixed it, which let Mantis start working again.