For anyone that is interested, I too was having issues debugging in VB.NET 2010 Express using Inventor 2011.
There is an Inventor.exe.config file in the "C:\Program Files\Autodesk\Inventor 2011\Bin" directory whose contents should be amended thus:
BEFORE
<?xml version="1.0" encoding="utf-8"?>
<!-- $Header:$ -->
<!-- This config file is copied to the Inventor bin\ folder by //inventor/Main/sources/AddInApps/CCClient/AddIn/CCV2/PostBuild.bat -->
<configuration>
<configSections>
<sectionGroup name="autodesk.inventor.content">
<section name="logging" type="System.Configuration.DictionarySectionHandler,system, Version=1.0.3300.0, Culture=neutral, PublicKeyToken=b77a5c561934e089, Custom=null"/>
</sectionGroup>
<section name="microsoft.web.services3" type="Microsoft.Web.Services3.Configuration.WebServicesConfiguration, Microsoft.Web.Services3, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
</configSections>
<appSettings>
<!-- Controls client cache allocation limit. MaxCachedObjects controls the maximum number
of cached objects before a purge is done. CachePurgeInterval controls how many objects
are removed when a purge is done -->
<add key="Connectivity.Content.MaxCachedObjects" value="500"/>
<add key="Connectivity.Content.CachePurgeInterval" value="100"/>
<add key="Connectivity.Content.MaxSearchResults" value="2500"/>
<!-- WebService timeout (in milliseconds)-->
<add key="WebServiceTimeout" value="1000000"/>
</appSettings>
<microsoft.web.services3>
<messaging>
<maxMessageLength value="51200"/>
<mtom clientMode="On" maxMimeParts="1024"/>
</messaging>
<security>
<!-- Specifies the time buffer used by WSE to determine when a SOAP message is valid.
set to the max of 24hr in seconds -->
<timeToleranceInSeconds value="86400" />
</security>
</microsoft.web.services3>
<!-- Since Inventor is an unmanaged application, we need to explicitly identify
the framework version it's to use. Otherwise, it will pick up the latest
version that's been installed -->
<startup>
<!-- The following specification works for both .NET 2.0 and .NET 3.0, since they share the same CLR.
.NET 3.0 installs both
C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727 (the CLR) and
C:\WINDOWS\Microsoft.NET\Framework\v3.0
The 'v3.0' folder contains WPF and some other components built on top of .NET 2.0.
Inventor won't start up if the following in changed to "V3.0" -->
<supportedRuntime version="v2.0.50727"/>
</startup>
</configuration>
AFTER
<?xml version="1.0" encoding="utf-8"?>
<!-- $Header:$ -->
<!-- This config file is copied to the Inventor bin\ folder by //inventor/Main/sources/AddInApps/CCClient/AddIn/CCV2/PostBuild.bat -->
<configuration>
<configSections>
<sectionGroup name="autodesk.inventor.content">
<section name="logging" type="System.Configuration.DictionarySectionHandler,system, Version=1.0.3300.0, Culture=neutral, PublicKeyToken=b77a5c561934e089, Custom=null"/>
</sectionGroup>
<section name="microsoft.web.services3" type="Microsoft.Web.Services3.Configuration.WebServicesConfiguration, Microsoft.Web.Services3, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
</configSections>
<appSettings>
<!-- Controls client cache allocation limit. MaxCachedObjects controls the maximum number
of cached objects before a purge is done. CachePurgeInterval controls how many objects
are removed when a purge is done -->
<add key="Connectivity.Content.MaxCachedObjects" value="500"/>
<add key="Connectivity.Content.CachePurgeInterval" value="100"/>
<add key="Connectivity.Content.MaxSearchResults" value="2500"/>
<!-- WebService timeout (in milliseconds)-->
<add key="WebServiceTimeout" value="1000000"/>
</appSettings>
<microsoft.web.services3>
<messaging>
<maxMessageLength value="51200"/>
<mtom clientMode="On" maxMimeParts="1024"/>
</messaging>
<security>
<!-- Specifies the time buffer used by WSE to determine when a SOAP message is valid.
set to the max of 24hr in seconds -->
<timeToleranceInSeconds value="86400" />
</security>
</microsoft.web.services3>
<!-- Since Inventor is an unmanaged application, we need to explicitly identify
the framework version it's to use. Otherwise, it will pick up the latest
version that's been installed -->
<startup>
<!-- The following specification works for both .NET 2.0 and .NET 3.0, since they share the same CLR.
.NET 3.0 installs both
C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727 (the CLR) and
C:\WINDOWS\Microsoft.NET\Framework\v3.0
The 'v3.0' folder contains WPF and some other components built on top of .NET 2.0.
Inventor won't start up if the following in changed to "V3.0" -->
[color=red] <!-- <supportedRuntime version="v2.0.50727"/> -->
<supportedRuntime version="v4.0"/>[/color]
</startup>
</configuration>
The changes I made are in RED.