A managed solution cannot overwrite the AttributeMap component with Id=[guid] which has an unmanaged base instance

Facing this message?

A managed solution cannot overwrite the AttributeMap component with Id=b648bf03-102f-e611-80d3-e1543fac8121 which has an unmanaged base instance. The most likely scenario for this error is that an unmanaged solution has installed a new unmanaged AttributeMap component on the target system, and now a managed solution from the same publisher is trying to install that same AttributeMap component as managed. This will cause an invalid layering of solutions on the target system and is not allowed.

Then you can quickly find the problematic mapping using the following query:

select SourceEntityName, SourceAttributeName, TargetEntityName, TargetAttributeName from AttributeMap am
left outer join entitymap em on em.entitymapid = am.EntityMapId
where am.AttributeMapId='b648bf03-102f-e611-80d3-e1543fac8121'

Just remove the mapping from the target system and reimport the solution and you're ready to go.