Make sure that you report that test center to Microsoft. There were some early teething issues with the virtualized lab exams, and the performance is highly dependent on the amount of bandwidth available to from the testing center. One of my colleagues had a similar experience, and the last I heard was the Microsoft was keen to address any issues at testing centers that were specific to the 83-series exams.
You can email Microsoft's Psychometrician, Liberty Munson, at liberty.munson@microsoft.com.
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CompTIA A+, Network+, Server+, Security+
MCTS:Windows 7
MCTS:Hyper-V
MCTS:System Center Virtual Machine Manager
MCTS:Windows Server 2008 R2, Server Virtualization
MCSE:Security 2003
MCITP:Server Administrator
MCITP:Enterprise Administrator