I have increased php memory up to 512M by modifying the php.ini in /usr/local/lib along with .htaccess, php.ini and cache.php in blog/wp-includes. Following these mods I stopped and restarted Apache. None of this changed anything: there are still no php errors in the Apache error log, and all I get is a blank screen although many other WordPress functions (e.g., blog entry) work.
I also get an error when launching wp-settings.php:
Warning: require(ABSPATHwp-includes/compat.php) [function.require]: failed to open stream: No such file or directory in /usr/local/apache2/stock-compass/htdocs/blog/wp-settings.php on line 238
Fatal error: require() [function.require]: Failed opening required 'ABSPATHwp-includes/compat.php' (include_path='.:/usr/local/lib/php') in /usr/local/apache2/stock-compass/htdocs/blog/wp-settings.php on line 238
What can I do that will make this work?