Looking at the default config for that version of WFFMs that node is not in the config (the wffm node is there but I can't see the modelFactory).
As Gatogordo suggests this node exists in previous versions of WFFMs:
<processor type="Sitecore.Forms.Mvc.Processors.SitecoreFormProcessor, Sitecore.Forms.Mvc"/>
<modelFactory type="Sitecore.Forms.Mvc.Data.ModelFactory, Sitecore.Forms.Mvc" singleInstance="true">
<param name="renderingContext" ref="wffm/renderingContext"/>
<renderingContext type="Sitecore.Forms.Mvc.Data.Wrappers.WrappedRenderingContext, Sitecore.Forms.Mvc" singleInstance="true"/>
<formDataManager type="Sitecore.Forms.Mvc.Data.FormDataManager, Sitecore.Forms.Mvc" singleInstance="true">
<param name="processorFactory" ref="wffm/formProcessorsFactory"/>
<formProcessorsFactory type="Sitecore.Forms.Mvc.Data.SitecoreProcessorFactory, Sitecore.Forms.Mvc" singleInstance="true"/>
So either your DLLs are old and expecting old config - or the installer is wrong and this config needs to be present in Sitecore.Forms.Mvc.config
I would redownload the installation package from the link above, unpack it and compare the DLL versions against your bin folder, also look for extra DLLs perhaps. If they all look correct, try adding that config node back in and see if it works.
Be worth logging this with Sitecore as well if the config on the installation package is incorrect.