No feasible equipment causes

Summary:

What are possible causes for the following error

Content (please ensure you mask any confidential information):

I tried to manually assign driver (linked to power unit and equipment) to a shipment and the equipment type is included the equipment group of the buy shipment.

Also the drivers isn't assigned to any other shipments.

Also need to know how to assign same driver on several shipments whether same start time or not.

Version (include the version you are using, if applicable):

OTM24C

Code Snippet (add any code snippets that support your topic, if applicable):