Hmm. Interesting for sure since as far as I know I have never seen a similar circumstance reported. I would first make sure you are using the latest Thunder. Like I said in my last response, make sure your server is properly configured as well. Check any custom code you have that may be interfering with view state, caching, etc. Clear your app_Data/sitefinity/logs and feel free to post back again if the error occurs with those log files. They may have some valuable info related to this issue.
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