We are currently using the Silverlight API version 3.0 and whenever we try to initialize an ArcGISDynamicMapServiceLayer from a 10.4 server we are getting InvalidCastException Unable to cast object of type 'System.String' to type 'System.Collections.ICollection'.

I know the latest (and final) Silverlight API is version 3.3, but upgrading breaks a lot of our existing code, and before spending any time trying to fix our code to upgrade to version 3.3 I was wanting to know if anyone else is having the same problems when running version 3.3

I've seen that other people have had the same problem https://geonet.esri.com/thread/173642, but I don't know what API version they were using.

If this is a known issue for the Silverlight API 3.3, then we would rather just stick with our current API version and continue putting our focus on moving away from Silverlight entirely.

2 Answers 2


I have received some feedback from other people on the geonet forums here https://geonet.esri.com/thread/173642, and it looks like they are having the same issues on Silverlight API 3.3, so I am going to assume that ArcGIS server 10.4 is not compatible with the Silverlight API in regards to Dynamic layers and it is very unlikely that this issue will be resolved by Esri, so our best course of action is to get off of Silverlight as fast as possible.


The unlikely happened, and apparently server 10.4 not working with Silverlight was a bug, and Esri has fixed the bug in version 10.4.1 (see same thread linked above for more details). I found a server running 10.4.1 to test against, and it did work at least in regards to this specific issue. I still believe the best course of action is to move away from Silverlight as fast as possible, but at least Silverlight can limp along for a little bit longer.


This doesn't answer your question directly, but the Silverlight API is scheduled to be retired in three months.

While technical support will be available for both APIs and viewers through June of 2016, maintenance of these products will be discontinued. Customers who develop with these products should begin exploring web solutions that are based on JavaScript or HTML5.

I would not worry about upgrading to 3.3 and focus on moving to another API.

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