This is a common Workflow error I’d observed on many MS Dynamics CRM environments while trouble-shooting their workflows:
The system could not log you on. This could be because your user record or the business unit you belong to has been disabled in Microsoft Dynamics CRM…
If you look into this error from the MS CRM System Jobs view (Settings >> System Jobs) – it shows a status of “Waiting”
The cause is simply the owner of this Workflow being disabled. It is an easy fix – reassign the workflow to another MS CRM User or re-enable the owner.
Some background: Many often, workflows are built by MS CRM Users that are temporary staffs such as consultants or contractors. And when they leave, the normal procedure is to disable their logins. Unfortunately, more often than not, the workflows that they had created remained under their ownership. And it usually takes some time before this issue is discovered and corrected.
As a good practice – once a workflow is validated, assign it to a permanent MS CRM User. There should always be a designated permanent MS CRM User/Administrator (a MS CRM Login that should be always be enabled) for a MS CRM production environment – if not, I’d highly recommend to define one today.
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Frank Lee, Microsoft CRM MVP since 2006
Workopia
Microsoft Dynamics 365 CRM Blog 
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