I opened the Default.aspx file fron DNN 4.5.1 and permitter Visual Webdevelopet 2005 Express to 'work out the details'.
The results are -
Error 1 It is an error to use a section registered as allowDefinition='MachineToApplication' beyond application level. This error can be caused by a virtual directory not being configured as an application in IIS. C:\Inetpub\DotNetNuke\WebSite\web.config 53
Error 2 Unrecognized tag prefix or device filter 'asp'. C:\Inetpub\DotNetNuke\Default.aspx 3 2 C:\Inetpub\DotNetNuke\
Error 3 Unrecognized tag prefix or device filter 'asp'. C:\Inetpub\DotNetNuke\Default.aspx 19 6 C:\Inetpub\DotNetNuke\
Warning 4 Validation (Internet Explorer 6): Attribute 'marginwidth' is not a valid attribute of element 'body'. C:\Inetpub\DotNetNuke\Default.aspx 21 94 C:\Inetpub\DotNetNuke\
Warning 5 Validation (Internet Explorer 6): Attribute 'marginheight' is not a valid attribute of element 'body'. C:\Inetpub\DotNetNuke\Default.aspx 21 110 C:\Inetpub\DotNetNuke\
Error 6 Element 'Form' is not a known element. This can occur if there is a compilation error in the Web site. C:\Inetpub\DotNetNuke\Default.aspx 23 10 C:\Inetpub\DotNetNuke\
Warning 7 withEvents variable 'Form' conflicts with property 'Form' in the base class 'Page' and should be declared 'Shadows'. C:\Inetpub\DotNetNuke\Default.aspx 1 1 C:\Inetpub\DotNetNuke\