Create Custom Modal Popup in ASP.Net

ramco1917 says:

ClientScript.RegisterStartupScript(this.GetType(), "Popup", "ShowPopUp('" + Title + "', '" + Text + "','" + Type + "');", true)

ClientScript.RegisterStartupScript is used to call the JavaScript function.

It is not used for calling the Server Side function.

So in the else condition call the ShowPopUp.

Or create a function in JavaScript and call using ClientScript.RegisterStartupScript.

For more details refer below article.

RegisterStartupScript: Call JavaScript function with parameters in ASP.Net using C# and VB.Net