We’ve recently encountered an issue whereby workflows on a SharePoint 2013 environment will stop running as expected and kick up the error “Could not deserialize object. The type ‘<Workflowname>.<Workflow actions>.<workflow Action>’ could not be resolved.”. This gave us quite the headache for a long while until we finally manged to find the root cause of this.
To fix this do the following:
1) Open up your web config file (usually stored C:\inetpub\wwwroot\wss\VirtualDirectories\<port name used>).
3) If you look just below this you should then see the below:
4) This is where your workflow dependencies will show and what is causing the issue. These will start with the following:
5) To fix this simply right click cut all of these and paste them above </targetFx>, for more clarification these will now show in between:
6) Depending on how big your SharePoint Farm it is best to maker sure all your web config files show the same thing therefore you will simply need to repeat the process.
7) Do an IISReset in CMD and away you go!