I got the same problem. Running ArcGIS Server 10.2.2. The Path solution presented above didn´t help for me.
Tested on three different machines so far, two physical development machines (windows 7) and on one virtual machine (windows server 2012)
Search service fails to initialize the GP-service. Looking in AGS Manager in search service Parameters - Indexing status, it says "indexing" but no items are added.
Using UNC-path to folders with shapefiles. Shared to everyone.
Server log says:
StartIndexing() failed. Utilities/Search.IndexGenerator
Can not create CLSID_ItemIndex. Utilities/Search.IndexGenerator
Can not create CLSID_JItemIndex. Utilities/Search.IndexGenerator
Bug reported in 10.1 SP1 (nim090528), still open.
Any news on this?