After replacing W3TC with the modified version of 0.9.2.5 mentioned above (http://www.wmiles.com/2013/01/03/w3tc-cache-preload-for-version-0-9-2-5) my problems get reduced to this error message only:
It appears Minify URL rewriting is not working. If using apache, verify that the server configuration allows .htaccess or if using nginx verify all configuration files are included in the configuration.
... and the page is finally accessible again!