NSURLSessionDownloadTask initiation in backgroundURLSession completionHandler

I have a situation where I need to download multiple files sequentially as each download depends on its previous downloaded file. (I am processing the file in background itself)

I am using NSURLSessionConfiguration backgroundSessionConfiguration.

There is a scenario where NSURLSessionDownloadTask initiates while the application is in background. This crashes the app with Assertion permittedbackgroundduration.

So, my question is, am I doing wrong by initiating the download task in background???

Thanks in advance, - Satya