SharePoint (and Project Server) Shenanigans

I was recently asked to help out a client who was having problems with standard Out Of the Box Approval workflow.

We checked the Farm and isolated the issue to one specific site collection, all other site collections were fine.

To resolve this we opened the site collection in SPD, open the All files section drilled into the _catalogs/wfpub folder, the folder for the Approval workflow was present but for some reason the wfconfig.xml file had been modified from the site definition (Shown by blue I symbol), once this file had been reset to the site definition workflows were working again.