Well, I ran into a problem with my captcha stuff on my blog, it wasn't working. Just displaying a red X. I am on a 2008 R2 server with IIS7.5 and .NET 4.0 64-bit. The fix was simple. I had to change the handlers in the web.config. Specifically the preconditions. The used to be integratedMode,runtimeVersionv2.0.

You can either change them to integratedMode,runtimeVersionv4.0 or just remove them.

In the section, remove the preCondition stuff from the entries pertaining to dotnetnuke. All of mine had DotNetNuke in them, as this is a pretty straight forward simple install of it.This is what my section looks like now

<handlers> 
  <remove name="WebServiceHandlerFactory-Integrated" /> 
  <add name="LogoffHandler*" path="Logoff.aspx" verb="*" type="DotNetNuke.Services.Authentication.LogOffHandler, DotNetNuke" /> 
  <add name="RSSHandler" path="RSS.aspx" verb="*" type="DotNetNuke.Services.Syndication.RssHandler, DotNetNuke" /> 
  <add name="LinkClickHandler" path="LinkClick.aspx" verb="*" type="DotNetNuke.Services.FileSystem.FileServerHandler, DotNetNuke" /> 
  <add name="CaptchaHandler" path="*.captcha.aspx" verb="*" type="DotNetNuke.UI.WebControls.CaptchaHandler, DotNetNuke" /> 
  <add name="UserProfilePageHandler" verb="*" path="User.aspx" type="DotNetNuke.Services.UserProfile.UserProfilePageHandler, DotNetNuke" /> 
  <add name="Telerik.Web.UI.WebResource" verb="*" path="Telerik.Web.UI.WebResource.axd" type="Telerik.Web.UI.WebResource, Telerik.Web.UI" /> 
  <add name="Telerik.Web.UI.ChartHttpHandler" verb="*" path="ChartImage.axd" type="Telerik.Web.UI.ChartHttpHandler, Telerik.Web.UI, Culture=neutral, PublicKeyToken=121fae78165ba3d4" /> 
  <add name="HtmTemplateFileHandler" verb="*" path="*.htmtemplate" type="DotNetNuke.HtmlEditor.TelerikEditorProvider.HtmTemplateFileHandler, DotNetNuke.HtmlEditor.TelerikEditorProvider" /> 
</handlers>