On a Dynamics 365 organization, when importing CRM 2016 solutions that contain the same Business Process Flows(OOTB or custom ones) that have been customized on the target with new stages on additional entities, a new layer is attempted to be created over the existing one which results in the following error:
A managed solution cannot overwrite the Attribute component with Id=<attributeid> which has an unmanaged base instance. The most likely scenario for this error is that an unmanaged solution has installed a new unmanaged Attribute component on the target system, and now a managed solution from the same publisher is trying to install that same Attribute component as managed. This will cause an invalid layering of solutions on the target system and is not allowed.
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