button click method isnt getting picked up...

 Hi all.
I recently reinstalled windows/visual studio etc etc..
I have a problem even just adding a button to a web page. I am programming in c# and I add a button to a page, called "btnTest" and then double click on it to add the event code to the back end. But when I now debug the page, it comes up with teh following error:
 CS1061:
'ASP.admin_login_aspx' does not contain a definition for
'btnTest_Click' and no extension method 'btnTest_Click' accepting a
first argument of type 'ASP.admin_login_aspx' could be found (are you
missing a using directive or an assembly reference?)
Any ideas why I would get this message? I have never come across it. The method which is auto added is as follows:
protected void btnTest(object sender, EventArgs e)
        ...