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IO_ERRORs are 90% of the time an issue related to one of two things:
1. You have a firewall blocking *prezi.com. Please allow an exception for *prezi.com in order to proceed.
2. You have not updated Flash to its most recent version. Please visit http://get.adobe.com/flashplayer/
Let me know if this helps and I am happy to assist you if you have any other questions.