WordPress Plug-In Install Problem

I encountered the following error when installing a new plug-in (edited for details):

Warning: include_once() [function.include]: Failed opening ‘##path-to-wordpress##/wp-content/plugins/twitter-for-wordpress/’ for inclusion (include_path=’.:/usr/share/php:/usr/share/pear’) in ‘##path-to-wordpress##/wp-settings.php on line 473

I’d installed the plug-in “manually” (that is, downloaded it  and unzipped it into the plug-ins directory).  Some quick web searching didn’t exactly point to the error.  Nor did looking at the wp-settings.php file line 473 (just a straightforward directory include … of a directory that’s already been confirmed to exist!).

Everything pointed to a permissions problem.  OK.  Checked the permissions … and they were, indeed, bad.  So I fixed up all the permissions (so that Apache and its friends could read the directory) … still the same error.  Even recycled Apache … still a problem.  Googling didn’t really help … one page was on point (but without a fix), and the rest of the hits were all on pages that were throwing this same error <g>.

Turns out that once you’ve started a plug-in install, if your permissions are bad, you’re hosed.  You need to remove, then re-install the plug-in.  I did this, which fixed the problem:

1. Moved the new plug-in directory out of the plugins folder.
2. Reloaded the admin plugins page … OK, error disappears.
3. Moved the new plug-in directory back in.
4. … voila, able to install and configure the plug-in.