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If you are publishing to a 10.2.1 server its a 10.2.1 service. Sync was in that release but there are necessary fixes in 10.2.2 that are not in 10.2.1 and could be why the Collector is failing to take it offline. Have you tried making a hosted service version and see if the app can take it offline?
I have 10.2.2 server and a 10.2.2 geodatabase with the feature service on a non-versioned feature class. I'm still getting the Failed to Create Replica message - it doesn't tell me anything else. I'm using a Tile package that I created and used very nicely in ArcGIS Mobile for Windows.
I was getting a error about Nulls until I took out the other layer in the map which was only Read only vector layer for info. Kinda buggy still!
I had the same issue and I found out that you cannot desactivate a field with index (the ones that have a star at the end in the attribute table).
Though they are not mandatory fields, as soon as they have an index, it will fail.
Hope this can help,