When trying to insert a GridFS record into a shard collection and replicateset cluster env using the below code getting error as mentined in the image

db.GridFS.Upload(mongoDocs.m_stream[docItem], mongoDocs.m_fileInfo[docItem].Name) 

We haven't created any index on the fs.chunks collection.

Error is :

can't use unique indexes with sharding  
ns:researchdocs.fs.chunks key: { files_id: 1, n: 1 }