Modal dialog box error

Because you are running an asp.net application and trying to show a messagebox in server-side code. if you are using the built-in webserver, effectively running as an interactive user account - using IIS as the server even on your development machine will raise the same issue).

There is no direct solution, the use of a messagebox which is raised in server-side code is illogical in a client-server situation such as a browser based application. There are basically two options that you can consider:

1) Modify your approach to allow you to use client-side script to display alerts using window.alert() for example before posting back to the server once everything is sorted
2) Modify your approach to end the processing server-side, emit relevant client-side script and html to display the alert on the client, then handle the continuation of processing on the server side.

Personally I would go with option 1 as it is generally the easiest (though not always easy).

OF course there is a third option which is to use a different mechanism for recording alerts generated in this way (or just don't do it!).

 
If you want to display a message I would use...

Response.Write("")

Hi, 

Using MsgBox is not intended to work in ASP.NET 2.0. If it works, it

will show a message box on the server rather than on the client machine and if you try to Show it you will get error 

that is Wrritten by you in your Question ( This is what Microsoft Says ) :)

You can Show Dialog box Like Below Code very Easily and Efficiently 

Dont Forget to Mark "Do you Like answer" it will give me some credits 

 protected void Button4_Click(object sender, EventArgs e)
    {
        Page.RegisterClientScriptBlock("ShowMessage", "<script>alert('Hello This is MessageBox')script>");
        
    }

Happy Coding :)

Hi,

U can specify servicenotification or DefaultDesktopOnly option in message box enumeration .

Specify like that

MessageBoxOptions.ServiceNotification
MessageBoxOptions.DefaultDesktopOnly