I was configuring Custom Errors in the web.config of my ASP.Net 2.0 application, and set it up as follows:

<customErrors mode="remoteOnly" defaultRedirect="~/Error.aspx">
  <error statusCode="403" redirect="~/AccessDenied.aspx" />
  <error statusCode="404" redirect="~/Error404.aspx" />
</customErrors>

I had found the syntax on MSDN. To my surprise, the applicationm wouldn't start, it told me there was something wrong with the value of the mode attribute.

So I went back to MSDN and noticed I had looked at the .NET Framework 1.1 documentation. Clicking on the corresponding 2.0 documentation, I found it had changed to initial Caps:

<customErrors mode="RemoteOnly" defaultRedirect="~/Error.aspx">

Duh! I guess my chances of getting this right the first time were remote only...