Windows Phone app exception: System.Windows.Markup.XamlParseException

I have a windows phone app which works fine in the emulator and on my test device (Lumia 520), but when published to the store it appears everyone is having issues with it. In my crash logs I see lots of the same error:

Problem Function: MS.Internal.XcpImports.TileHostV2_SetNativeContentProvider
Exception Type: System.Windows.Markup.XamlParseException

Stack Trace:
"Frame    Image                         Function                                                      Offset        
0        system_windows_ni             MS.Internal.XcpImports.CheckHResult                           0x001c1f04    
1        system_windows_ni             MS.Internal.XcpImports.TileHostV2_SetNativeContentProvider    0x00000054    
2        system_windows_ni             MS.Internal.TileHostV2.BindToAgWebBrowserControl              0x00000028    
3        microsoft_phone_interop_ni    Microsoft.Phone.Controls.WebBrowserInterop..ctor              0x0000008e"

The problem is, this doesn't give me a great deal to go on. It doesn't appear to be related to pretty much anything in my code that I can relate to. I can see the WebBrowser component seems to be having an issue in its constructor maybe, but how can I possibly resolve that (if it is the cause)?

Has anyone seen this error before or have any idea how to diagnose it?

Thanks

Check if you have set the ID_CAP_NETWORKING capability in the WMAppManifest.xml file.

Apparently MS.Internal.XcpImports.TileHostV2_SetNativeContentProvider needs it to download map tiles when executed on non-development devices.