I had a problem with a workflow that was failing on a send email step.There was no clear reason as to why the step should fail. The details message of the workflow log had this error:
Cannot create the given type without the required parameters.
Not especially helpful. However, a search revealed that others had seen this issue before and provided a resolution of deactivating the workflow, removing the recipients of the email, saving the workflow and then adding the recipients back,
I am grateful and acknowledge the blogs at https://community.dynamics.com/crm/b/mscrmhowtoforendusersandadministrators/archive/2015/01/21/workflow-waiting-error-on-email-creation-step and https://rule30.wordpress.com/2014/04/page/2/ for providing a resolution.