I have recently switched over to VS 2008, and at first I was just continuing to target the 2.0 framework.  I thought I would try to make the switch to 3.5, and changed all the projects in my solution to target it.  It modified the web.configs of the sites to include a system.codedom section.  The problem is when I go to build the solution now, I get a compile-time error saying "Child nodes are not allowed" ... which points to that new section in the web.configs:

  <system.codedom>
    <compilers>
      <compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CSharp.CSharpCodeProvider,System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" warningLevel="4">
        <providerOption name="CompilerVersion" value="v3.5"/>
        <providerOption name="WarnAsError" value="false"/>
      </compiler>
      <compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" type="Microsoft.VisualBasic.VBCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" warningLevel="4">
        <providerOption name="CompilerVersion" value="v3.5"/>
        <providerOption name="OptionInfer" value="true"/>
        <providerOption name="WarnAsError" value="false"/>
      </compiler>
    </compilers>
  </system.codedom>

 I found a ton of posts that said all you needed to do to fix this is install some updates that could be found on the VS 2008 DVD, but I have installed those and it is still not compiling.

 I don't think it is specific to my solution, because if I just create a new web site from scratch in VS 2008 and try to compile it ... I get this same error.  It might be something specific to x64 machines, because another developer I work with is running on x86 and never ran into this issue.  Any ideas?

Please have a look at this thread: http://forums.asp.net/p/1186009/2024111.aspx#2024111

Yeah, I appreciate your reply ... but I have already seen that post.  Really since this is a compile-time error, I don't think it has anything to do with IIS.  In fact, since I am kind of at a stand still until I get this figured out, yesterday I uninstalled Visual Studio, the .NET Framework, IIS, and anything else on my machine that could be remotely related.  I then reinstalled everything (except IIS), got all of the possible Windows Updates (including the ones on the VS DVD) ... and it is still happening.  So there is no way the issue is with IIS, because it is happening and I still don't have IIS installed on my machine.

 Like I said, I appreciate your shot at helping me ... but I just want to be clear that this is an issue with VS 2008 and not IIS.  Many of the posts I saw (like the one you pointed me to) seem to point to IIS as the problem ... but I don't really think that is even possible.

I opened a phone support case with Microsoft, and they first sent me to the general level 1 support-type people then the developer support, then the ASP.NET Team, then the Visual Studio & .NET Framework setup people, then on to the Visual Studio team ... and after a 5 hour support call that is still where it is.  I believe some members of the Vista or Visual Studio team are reviewing some sfc log files from my machine.  I will update this post when/if we figure out what is going on.  But one thing is for sure ... it is either a Visual Studio or .NET Framework issue (not IIS) that is probably specific to Vista x64.  If anyone has any ideas I could try in the mean time, I am open to them.

I'm seeing the same issue. 

Here's is what I have tried, WITHOUT luck:

- installing the two files on the cd that have resolved the problem for others.

- uninstalled VS 2008 and installed the trial VS 2008

Here's my environment:

- Vista 32bit

- VS 2005 installed

My next step:

Remove VS 2005 and the trial, then reinstall. 

 Any suggestions from other dealing with the same? 

I talked with the support team for VS 2008 yesterday, and they suggested a fix ... but unfortunately it didn't work.  They thought that somehow the C:\Windows\SysWOW64\inetsrv\Microsoft.Web.Administration.dll had been corrupted or was out of sync with the rest of the dlls, so they asked me to replace it with a copy of the same file from a machine that wasn't having this issue.  I did that, and I still got the same error.

Since it did take Microsoft a couple days to get back to me from my original phone call, I went ahead and did what I hate most ... reinstalled Windows from scratch.  Yeah I know, it sucks.  But, although Microsoft admits this is a bug they still don't know if it is an issue with Visual Studio 2008, .NET Framework 3.5, Windows Vista x64, or IIS 7.  So since it is such a complex issue, I couldn't just pick up a book and read for the next couple weeks while they try to sort this out ... because this was on my production development machine. 

I actually installed another drive and put the new Windows install on it, so I can still boot into the "broken" version for now.  The support guys said they will look into it some more and call me tomorrow (2/15/08) and let me know what they found and what else I can try to fix it.  If they have any suggestions that sound like they would come close to working, I will post them on here.  As much as I hate saying this ... if I were you, I would just flatten the machine and reinstall.  I think I have tried everything else.  I tried to avoid it like the plague, but looking back I really just wasted a couple days and eventually ended up doing it anyway.

Well, Microsoft closed the case last week ... no resolution.  They didn't ever come back and suggest any other changes or stuff to try.  I guess if you are reading this thread that is bad news.  After I reinstalled Windows and all my programs, VS built the same exact files without error.  Don't know what to say.  I hate issues like this where you never really figure out what was causing the problem.