Why am I seeing this error page and not a TYPO3 error?

This error page was specially constructed to be far more informative than the default TYPO3 errors - in order to specifically debug problems with Fluid page templates. Since the error message itself is based on an Exception, this page can provide additional troubleshooting info based on your specific TYPO3 site's settings and templates.

Can I disable this error page

Yes, of course. There are two ways to do that:

1. You can override this template with one containing a custom error page by setting plugin.tx_fluidpages.view.templateRootPath to another path also containing the Error.html file. If your custom error page uses Partials and/or Layouts, remember to add those paths as well - also under the plugin.tx_fluidpages.view location.
2. You can set plugin.tx_fluidpages.settings.displayErrors = 1 but beware; this has the effect that the Exception is thrown as it normally would be - leaving it up to the TYPO3 error handler (and its settings!) to take care of reporting, which means among other things the reporting is affected by the Install Tool's displayErrors setting.

Why is this error special?

The error occurred while initialising the View of a Flux enabled controller, most likely the Fluidpages controller - normally such errors will be caused by one of the following:

1. No configuration exists, syntax errors in configuration - or configuration is inaccessible. Check that you have included at least one page template and that you have selected it for the top-level page (as well as defined which template subpages should use).
2. The configuration is incomplete - for example missing one or more path definitions when the templates themselves require them to be present (i.e. rendering a Partial template will require the partialRootPath setting to be present).
3. The template itself contains errors - if this is the case, the Exception message above should help you locate the exact cause of the problem.

NB: This page template is EXT:fluidpages/Resources/Private/Templates/Page/Error.html and it is being used because no custom error page could be detected and used - which usually points to configuration missing completely.