You learn something new every day. I just don't have time to blog about it every time. This one seemed significant enough.
I'm writing a little ASP.NET app to keep up my web skills since my day job keeps me busy cranking out back-end code. For the first time, I've tried playing with themes. I wanted to assign a theme based on a user configuration, so I unwittingly assigned it in the Page_Load event.
Bo no... Nasty little error message telling me I can't do that, so a bit of digging revealed it has to be done earlier in the life of the page.
protected void Page_PreInit(object sender, EventArgs e)
this.Theme = GetTheme();
That did the trick.