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The request page cannot be accessed because the related configuration data for the page is invalid
Cannot read the configuration file due to the insufficient permisons

It is give error in IIS 7.0 or higher (i.e. Win7 or Win2003). It happens because there are no permisons to the user who run the applicacion. 
In order to solve you could:
  1. Make sure that IIS has the .NET Framework enabled. You can check the default website properties and make sure there is an ASP.NET entry in there. If there is not, you need to register the .net framework which you can do by running C:\Windows\Microsoft.NET\Framework\v2.0.50727\aspnet_Regiis -i

    If use Framework 4.5, you need register with: ​dism /online /enable-feature /featurename:IIS-ASPNET45 /all
  2. Change the user over the Application POOL, configured in this virtual directory;  
  3. Through Windows Explorer to increase the default user's permissions (such as ASPNet, or Everyone or Authenticated User). Take into account the risk to give more permissions to predefined users of the system;
  4. It could happen in IIS 8.5, installed with windows 8.1.In this case be sure that, there aren't duplicate definitions of mime type, between IIS and web.config file;
  5. Also, maybe HTTP Activation of WCF is not installed. Install it via Windows Features;
  6. Please check URLRewrite or here
  7. Enabled a configuration section in config files. More information here or here;
Other solutions: http://support.microsoft.com/kb/942055/es