How to rebuild registry table?
The absolutely easiest way to do it, is to enable any module, as that will do it for you. Of course, if you need to rebuild the registry, generally speaking the UI might be unavailable, but drush en [modulename] might be all you need.

If that's not enough, Registry rebuild makes it trivially easy to rebuild the registry. The easiest way to do it, is to install it as a drush extension.

Install the extension, and run drush rr.

The module page has detailed installation instructions and also shows how to run it without drush if necessary.