The reason for this is incorrect assembly reference in manifest.xml, which results in invalid URL for IMembershipCondition element, where binary name has an extra .dll suffix in CAS policy file, just like in the file excerpt below:

C:\Program Files\Common Files\microsoft shared\Web Server Extensions\12\CONFIG\wss_custom_wss_mediumtrust_guid.config

   ...
  <CodeGroup version="1" PermissionSetName="mycustomwebpart.wsp-12345678-90AB-1234-5678-90ABC3456-1">
    <IMembershipCondition version="1" Name="MyCustomWebPart" Url="$AppDirUrl$/bin/MyCustomWebPart.dll.dll" />
  </CodeGroup>


The solution for this problem is relatively simple:

- in your Visual Studio open WSP View pane, click Refresh button to update solution files

- open manifest.xml and in <Assembly> element remove extension ‘.dll’ from Assembly Name attribute:

<Solution ...>
  ...
  <CodeAccessSecurity>
    <PolicyItem xmlns="http://schemas.microsoft.com/sharepoint/">
      ...
      <Assemblies>
        <Assembly Name="MyCustomWebPart" />
      </Assemblies>
    </PolicyItem>
</Solution>


Additionally, while editing manifest.xml if you like to grant your web part additional security privileges you might need to add a few lines to PermissionSet element. In particular, if you are using MOSS Search or Search Server functionality, such as KeywordQuery or FullTextSqlQuery classes you would need RegistryPermission and FileIOPermission lines.

<PermissionSet class="NamedPermissionSet" version="1" Description="Example">
...
<IPermission class="System.Security.Permissions.RegistryPermission, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" version="1" Unrestricted="true" />
<IPermission class="System.Security.Permissions.EnvironmentPermission, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" version="1" Unrestricted="true" />
<IPermission class="System.Security.Permissions.ReflectionPermission, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" version="1" Unrestricted="true" />
<IPermission class="System.Security.Permissions.FileIOPermission, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"version="1" Unrestricted="true" PathDiscovery="*AllFiles*" />
</PermissionSet>


Additional resources:

• MSDN: Administrator and Developer Guide to Code Access Security in SharePoint Server 2007
• MSDN: Solution Schema
• MSDN: Securing Web Parts in Windows SharePoint Services
• BlueDog Limited post: Code Access Security policies within SharePoint v3

Microsoft SharePoint product team is blowing all bells and whistles, announcing SharePoint 2010, and how important it is to switch to 64-bit environment, while poor SharePoint 2007 left in the dust and crippled with the only development extension working on 64-bit, which is still in CTP phase Visual Studio Extensions 1.3 (March 2009 CTP).

VSeWSS 1.3 was promised almost half a year ago to become a final release in the spring of 2009, and later on in one of the dev blogs mentioned July 2009 release date, but up to this date there hasn’t been any final version announcement or releases yet.

Also, if you are looking for more information and code snippets, you may still find useful referring to the samples that come with Visual Studio Extensions 1.1 for Visual Studio 2005 User Guide, which have been removed from 1.3 release.

I’m keeping my fingers crossed for the new release to come soon, while blaming it all for the recession…