How do you identify part of the ViewState is lost? Are you getting ViewState deserialization exceptions of some sort, or the data in your ViewState is lost? If you are getting any errors, can you, please, post the error message and stack trace, so that we can try to identify what's causing the issue. Also, are you getting this in development, or when running on production environment. If the latter, are you, by any chance, using any webfarm / load-balancing scenarios with multiple nodes?
Any further info you believe might be helpful is appreciated.
the Telerik team
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