Debug and fix Unity iOS app

I have had an android application built in Unity 3D, which takes assets from a web server in 7zip format, and then extracts it in the app and allows the user to search the assets within the app. Converting the app to iOS, it builds, and downloads assets, but won't extract the assets within the app, with an error coming up in xcode mentioning a null reference. I suspect that it is a stripping issue, but I don't know enough about iOS developing to pinpoint the problem. I can send you the code for you to have a look at, to see whether you think its something that you can help me with.