Geting error while executing the Set-WebConfigurationProperty cmd in powershell

Hi All

could any one help me in resolving the error while executing the following command in powershell

Set-WebConfigurationProperty -filter /system.webServer/security/authentication/AnonymousAuthentication -PSPath "iis:\" -Location "Default Web Site/IOWebServicesDemo" -name enabled -value false

i am getting the following error:

Set-WebConfigurationProperty : Filename: \\?\C:\Program Files (x86)\PST\Portrait IO\WebServicesDemo\web.
config
Line number: 80
Error: The configuration section 'system.web.extensions' cannot be read because it is missing a section
declaration

At line:1 char:30
+  Set-WebConfigurationProperty <<<<  -filter /system.webServer/security/authentication/AnonymousAuthent
ication -PSPath "iis:\" -Location "Default Web Site/IOWebServicesDemo" -name enabled -value false
    + CategoryInfo          : NotSpecified: (:) [Set-WebConfigurationProperty], COMException
    + FullyQualifiedErrorId : System.Runtime.InteropServices.COMException,Microsoft.IIs.PowerShell.Prov
   ider.SetConfigurationPropertyCommand

in the web.config file i have 'system.web.extensions' section with all commented configrations. i had made sure the app pool is set to the dot net 4.0.

in the proc monitor i can see that the CreateFileMapping operation on the web.config file is failing with FILE_LOCKED_WITH_ONLY_READER--- SYSNC_TYPE: SYNC_TYPE CREATE SECTION,PAGE PROTECTION

however if i will comment out the 'system.web.extensions'  section in the web.config file it works fine for me.

i am using visual studio 12 on windows 7 with windows update on.

regards

Mukesh Vashisth