I got error message while I am doing installation process. Right After I enter the config password.

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I did all requirments for installation at given the document.

http://forum.kemalburakyilmaz.com/install/ 

Server Error in '/YAF' Application.

Cannot save the YAF.ConfigPassword to the app.config file. Please verify that the ASPNET user has write access permissions to the app.config file. Or modify the app.config "YAF.ConfigPassword" key with a plaintext password and try again.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Exception: Cannot save the YAF.ConfigPassword to the app.config file. Please verify that the ASPNET user has write access permissions to the app.config file. Or modify the app.config "YAF.ConfigPassword" key with a plaintext password and try again.

Source Error:

The source code that generated this unhandled exception can only be shown when compiled in debug mode. To enable this, please follow one of the below steps, then request the URL:

1. Add a "Debug=true" directive at the top of the file that generated the error. Example:

<%@ Page Language="C#" Debug="true" %>

or:

2) Add the following section to the configuration file of your application:

Note that this second technique will cause all files within a given application to be compiled in debug mode. The first technique will cause only that particular file to be compiled in debug mode.

Important: Running applications in debug mode does incur a memory/performance overhead. You should make sure that an application has debugging disabled before deploying into production scenario.

Stack Trace:

[Exception: Cannot save the YAF.ConfigPassword to the app.config file. Please verify that the ASPNET user has write access permissions to the app.config file. Or modify the app.config "YAF.ConfigPassword" key with a plaintext password and try again.]

YAF.Install._default.Wizard_NextButtonClick(Object sender, WizardNavigationEventArgs e) +375

System.Web.UI.WebControls.Wizard.OnNextButtonClick(WizardNavigationEventArgs e) +108

System.Web.UI.WebControls.Wizard.OnBubbleEvent(Object source, EventArgs e) +418

System.Web.UI.WebControls.WizardChildTable.OnBubbleEvent(Object source, EventArgs args) +19

System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args) +37

System.Web.UI.WebControls.Button.OnCommand(CommandEventArgs e) +118

System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +166

System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10

System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13

System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +36

System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1565

I checked for write permission. its there, but getting this error.

Manually open app.config, and enter your desired configuration password into it (very first setting in the file), then save it.

When you run /install again, it will ask you for the password rather than prompt you to pick one.