MongoDB.Driver.MongoCommandException: Command insert failed: WriteConflict.

I have a NServiceBus endpoint and using MongoDB for persisting my Data . My application installed in QA environment on 20 machines (Which means all services are running together) . I have the same situation in Production environment . The only difference between Prod and QA is that in Prod we enabled replica set while in QA we do not . When I run my application with the same situation in both environments , everything in QA is fine but in prod I receive this error : MongoDB.Driver.MongoCommandException: Command insert failed: WriteConflict. couple you please help me in this regards?