I'm running WP 3.1.2 on an Apche server with the latest PHP installed. My WP is setup for a subdirectory multisite. The themes for the sites are usually a modified TwentyTen theme.
After installing a new plugin, I activate per site, not network, and I'm able to then click through to a few links in the admin UI before I'm prompted with an error starting with Warning: require_once
It doesn't matter what plugin is installed or how it's activated (per site or network). I have verified that the "missing file" is where it should be. I am using the latest version, most of them have been updated with in the past month or so and as per the official WP forum for the plugins, other users claim them to work properly.
It's becoming a real nuisance to have to go into every plugin and hard code the directory to each plugin file. I have tried reinstalling all the WP core files to no avail.
Has anyone else seen this or know how to fix it?
Edit: On a completely different domain with a brand new install of WP on a new database, I'm seeing hte same thing. Any new plugin install shows a missing file error. This is extremely annoying and I need to fix it. I suspect it's something within Apache but not sure.