This is a Strict Standards error. It does not prevent execution of the page.
However, it looks like Widget Framework changed the renderer signature in a recent version. This is unfortunate, since the change breaks all widgets that other add-ons have created, and Widget Framework does intend for other add-ons to create widgets.
The only way around this is to create two versions of the class: one for versions before the change was made, and one for newer versions. But I will need to know from the developer the exact version number of the framework when the signature of the ::render method was changed, and the author's intended programmatic way of detecting that version, ideally without queries (I cannot find a version constant on the Core class). If signatures of other methods are changed, I would need to know the versions of those as well.
EDIT: I checked the current public release (2.5.9) and it still uses the old signature.
In the mean time, you can edit
library/vw/WidgetFramework/CodeEventListener.php, and comment out this line:
Code:
$renderers[] = 'vw_WidgetFramework_WidgetRenderer';
After doing that, you will not be able to deal with VaultWiki widgets in Widget Framework. It seems like there has been a massive update, and the signature of the render method might be the tip of the iceberg.