Problem upgrading from .NET 1.1 to .NET 3.5

[Tom P.]

I'm getting an error on pregenerated code when I try to upgrade a
website from .net 1.1 to .net 3.5

The error is as follows:

'ASP.usercontrols_header_ascx.SupportAutoEvents': no suitable method
found to override

I've googled and all I found was an old post telling someone to remove
all the "namespace" declarations. Well, I did and I'm still getting
the error.

Any help would be great!

Tom P.