Tried my first web deployment project today after installing latest. What I think is a simple use of it was to replace the system.web section with system.web=release.config.

However the deployment project balks with an error:

Doesn't matter whether UseExternalConfigSource is true or false. As well Release.config has only a system.web section.

 My web.config file as found in the deployment directory (copied from web project by the build) certainly has a system.web section and is displayed verbatim below with some of the comments shortened but not removed (in case comments are not being parsed properly). It seems like Web Deployment 2.0 cannot do basic parsing of a pretty close to standard Ajax web.config file. I cannot see any errors in the web.config below nor does VS report any. Not very useful add-in, if basic functionality is broken. My purpose was to turn tracing off, but since trace is used in multiple sections, replacing the whole section was the only logical option.

<?xml version="1.0"?>

<configuration xmlns="http://schemas.microsoft.com/.NetConfiguration/v2.0">

<!-- All *****************-->

<!--******************** Required *****************-->

<configSections>

<sectionGroup name="system.web.extensions" type="System.Web.Configuration.SystemWebExtensionsSectionGroup, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35">

<sectionGroup name="scripting" type="System.Web.Configuration.ScriptingSectionGroup, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35">

<section name="scriptResourceHandler" type="System.Web.Configuration.ScriptingScriptResourceHandlerSection, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" requirePermission="false"/>

<sectionGroup name="webServices" type="System.Web.Configuration.ScriptingWebServicesSectionGroup, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35">

<section name="jsonSerialization" type="System.Web.Configuration.ScriptingJsonSerializationSection, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" requirePermission="false" />

<section name="profileService" type="System.Web.Configuration.ScriptingProfileServiceSection, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" requirePermission="false" />

<section name="authenticationService" type="System.Web.Configuration.ScriptingAuthenticationServiceSection, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" requirePermission="false" />

</sectionGroup>

</sectionGroup>

</sectionGroup>

</configSections>

<!--******************** Required *****************-->

<!-- This .... is accessing. -->

<connectionStrings>

<add name="PGEN_IntranetConnectionString" connectionString="Data Source=jbxsa522;Initial Catalog=PGEN_Intranet;Integrated Security=True" providerName="System.Data.SqlClient"/>

</connectionStrings>

<!--******************** Required *****************-->

<appSettings>

<add key="ApplicationId" value="142"/>

<add key="ApplicationName" value="Documentum Linker"/>

<add key="ApplicationStyle" value="_css/style.css"/>

<add key="ApplicationSecure" value="false"/>

<add key="dmUsername" value="zzzdmano"/>

<add key="dmPassword" value="dmanon2003"/>

<add key="dmDocbase" value="PGD"/>

<add key="defaultTypeName" value="dm_sysobject"/>

</appSettings>

<system.web>

<!--

After some experimentation, I found that while you cannot replace system.web section you can replace the connectionStrings section and other sections. This doesn't make a lot of sense hard coding nodes in an XML file that you can and cannot replace, plus an incredibly misleading error message when you try. The documentation on MSDN does not say anything about which sections you can and cannot replace, and this is probably a developer error in not treating the file like an XML file with a hiearchy of XML nodes. That should have been a piece of cake with standard XML functions, to remove a node and add a new one.

My suggestion for the syntax for the replacement should be a hierarchry of nodes to replace ANY node like "configuration/system.web/trace=trace.config". This does not work now even though I have seen examples suggesting there is a hiearchy.

The reason you can't replace system.web is that technically it isn't a configuration section: if you look in machine.config, you'll see that it is in fact a sectionGroup:

     <sectionGroup name="system.web" type="System.Web.Configuration.SystemWebSectionGroup, System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a">
      <section name="anonymousIdentification"
     ...

However you can replace sections within system.web using the syntax you specify, except that you shouldn't specify the top-level configuration node:

- system.web/trace=trace.config
- system.web/compilation=compilation.config
... etc ...

The reason you can't replace a sectionGroup is that the add-in assembly Microsoft.WebDeployment.Tasks.dll is using the API exposed by System.Configuration.Configuration / System.Configuration.ConfigurationSection etc to do the replacement - and this API only works with configuration sections.

I agree with you that it would be better to be able to replace any node in the config file: for the purposes of replacement the distinction between a sectionGroup and a section is rather arbitrary.  This could be done my modifying Microsoft.WebDeployment.Tasks.dll to use an XML API (XmlDocument etc) to do the replacement.

 I need to custom replace the sessionState property depending on the configuration. When I try to use 'system.web/sessionState=App_Data\sessionstate.config', I encounter the same error about a missing section:

 Error    5    web.config(1): error WDP00002: missing section system.web/compilation.

Any ideas on what else I could try here? 

I'm having the same issue -  I need to change some elements within system.web but pointing to system.web/compilation or system.web/identity produces the same missing section error...