So this is a Web application in c#.net
Well then you cannot use the Messagebox. This function / method
is used within an windows application
As mention earlier , you can solve this by using Javascript or ms.Ajax (Popup /modalpopup)

Hmmm Fine....
In C# we have to use script for messageBox.Okay let me do.
Tnx...

Select the function name "MsgBox", right click and from the menu select Go to Defenition and post the fuction defenition here. I suppose its a user defined function

Hi again

I yust wonder who this could be done..
Do as i told over.. in button click method

then select: project -> add reference
Then scroll down to System.Windows.Forms and select this.
Press ok

Hi,

I dont think what Frank is saying will work when deployed (But i will gladly be proven wrong as i would like to be able to use the messagebox functionality in an asp.net app). The messagebox will throw an exception because you can not show a modal form on a clients machine when it is created server side. The only real option avaliable is to Use javascript or Ajax as someone has mentioned earlier in this thread.

I must say i have never tried this before
So Yes, the best right way is by javascript..

Page.ClientScript.RegisterClientScriptBlock(typeof(Page), "SCRIPT", string.Format("alert('Hello World')"), true);