If you open the .aspx file and switch between design view and html view and
back it will prompt VS to check the controls and add any that are missing to
the designer file.
In VS2013-15 there is a Convert to Web Application command under the Project menu. Prior to VS2013 this option was available in the right-click context menu for as(c/p)x files. When this is done you should see that you now have a *.Designer.cs file available and your controls within the Design HTML will be available for your control.
PS: This should not be done in debug mode, as not everything is "recompiled" when debugging.
Some people have also reported success by (making a backup copy of your .designer.cs file and then) deleting the .designer.cs file. Re-create an empty file with the same name.
There are many comments to this answer that add tips on how best to re-create the designer.cs file.
You should rather use the ScriptManager class, since the Page.ClientScript property is deprecated...
The ClientScriptManager class is new in ASP.NET 2.0 and replaces Page class methods for managing scripts that are now deprecated.
Reference: MSDN - Page.ClientScript Property
The advantage with ScriptManager is that it works with asynchronous postbacks, so if you are using AJAX it will not work with the ClientScriptManager.
Your code would look like this:
ScriptManager.RegisterStartupScript(this, this.GetType(), "ShowPopup", "showCheckOutPopIn('Livraison',556);", true);
Note also that if you are using AJAX and have a piece of javascript code, that you want executed on multiple postbacks, then you should refer to your UpdatePanel in the firstargument e.g.:
ScriptManager.RegisterStartupScript(MainUpdatePanel, typeof(string), "ShowPopup", "showCheckOutPopIn('Livraison',556);", true);
Best Answer
Have you tried window.scrollTo(0, 0); ?
If you have, perhaps combine in with setTimeout
Although I expect this might produce some ugly jumping around.
An alternative would be to hook into the EndRequest event handler