I'm using an infragistics control that's targeted at ASP 3.5 libraries and after compiling under VS2008 [not touching the 5.0.0 libraries], I got an error that referred to 2.0 libraries:

error BC32206: Indirect reference is being made to assembly System.Web.Extensions version 3.5.0.0, which contains 'Infragistics.Web.UI.EditorControls.WebSlider'. This Project references a prior version of System.Web.Extensions version 1.0.61025.0. To use 'Infragistics.Web.UI.EditorControls.WebSlider', you must replace the reference to System.Web.Extensions with version 3.5.0.0 or higher.

Fair enough, I thought. I'll recompile the DNN libraries with all the dlls targeting the 3.5 framework ['My Project'>>Compile>>Advanced Compile options] as well as changing the references to the 3.5.0.0 version of System.web.extension ['MyProject'>>References].

So I did a clean install, changed the target and compiled [all good]. I also replaced all instances of "System.Web.Extensions, Version=1.0.61025.0" with the 3.5.0.0 version in the web.config.

Ran the install - and got an error:
System.NullReferenceException: Object reference not set to an instance of an object. at DotNetNuke.UI.Utilities.MSAJAX.get_IsInstalled() at DotNetNuke.UI.Utilities.MSAJAX.RegisterStartupScript(Page objPage, String Key, String Script) at DotNetNuke.UI.Utilities.ClientAPI.RegisterStartUpScript(Page objPage, String key, String script) at DotNetNuke.Framework.DefaultPage.InitializePage() in C:\Users\Duncan\Websites\DNN-5\Website\Default.aspx.vb:line 202 at DotNetNuke.Framework.DefaultPage.Page_Init(Object sender, EventArgs e)

Can someone point me in the right direction???

regards,
Duncan.