Topology activation failed - SharePoint 2013
I got the following error when try to modify existing topology by adding new Search Index Component
by this command
New-SPEnterpriseSearchIndexComponent
The reason for this because the index folder
(Default Path is
C:\Program Files\Microsoft Office Servers\15.0\Data\Office Server\Applications\Index)
is not empty so to fix this issue you need to reset Index from Search Administration.