I have similar problem with Word 2007 add-in made with VSTO 2005 SE, but was able to get the error message.
Word 2007 B2TR , AddinLoader.dll version 8.0.50727.444, , add-in folder in trusted location, PIAs installed. I have tried it on several different VMware setups and always get the same message.
Anyway, when I run Word with VSTO_SUPPRESSDISPLAYALERTS=0, the following message pops out and the add-in LoadBehaviour is back to 2:
Office document customization is not available
Could not load file or assembly 'Word Add-in, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. Failed to grant permission to execute. (Exception from HRESULT: 0x80131418)
************** Exception Text **************
System.IO.FileLoadException: Could not load file or assembly 'Word Add-in, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. Failed to grant permission to execute. (Exception from HRESULT: 0x80131418)
File name: 'Word Add-in, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' ---> System.Security.Policy.PolicyException: Execution permission cannot be acquired.
at System.Security.SecurityManager.ResolvePolicy(Evidence evidence, PermissionSet reqdPset, PermissionSet optPset, PermissionSet denyPset, PermissionSet& denied, Boolean checkExecutionPermission)
at System.Security.SecurityManager.ResolvePolicy(Evidence evidence, PermissionSet reqdPset, PermissionSet optPset, PermissionSet denyPset, PermissionSet& denied, Int32& securitySpecialFlags, Boolean checkExecutionPermission)
at Microsoft.VisualStudio.Tools.Applications.Runtime.AppDomainManagerInternal.HandleOnlineOffline(Exception e, String basePath, String filePath)
at Microsoft.VisualStudio.Tools.Applications.Runtime.AppDomainManagerInternal.LoadStartupAssembly(EntryPoint entryPoint, Dependency dependency, Dictionary`2 assembliesHash)
at Microsoft.VisualStudio.Tools.Applications.Runtime.AppDomainManagerInternal.ConfigureAppDomain()
at Microsoft.VisualStudio.Tools.Applications.Runtime.AppDomainManagerInternal.LoadAssembliesAndConfigureAppDomain(IHostServiceProvider serviceProvider)
at Microsoft.VisualStudio.Tools.Applications.Runtime.AppDomainManagerInternal.LoadEntryPointsHelper(IHostServiceProvider serviceProvider)
************** Loaded Assemblies **************
mscorlib
Assembly Version: 2.0.0.0
Win32 Version: 2.0.50727.42 (RTM.050727-4200)
CodeBase: file:///C:/WINDOWS/Microsoft.NET/Framework/v2.0.50727/mscorlib.dll
----------------------------------------
Microsoft.VisualStudio.Tools.Applications.Runtime
Assembly Version: 8.0.0.0
Win32 Version: 8.0.50727.444
CodeBase: file:///C:/WINDOWS/assembly/GAC_MSIL/Microsoft.VisualStudio.Tools.Applications.Runtime/8.0.0.0__b03f5f7f11d50a3a/Microsoft.VisualStudio.Tools.Applications.Runtime.dll
----------------------------------------
System
Assembly Version: 2.0.0.0
Win32 Version: 2.0.50727.42 (RTM.050727-4200)
CodeBase: file:///C:/WINDOWS/assembly/GAC_MSIL/System/2.0.0.0__b77a5c561934e089/System.dll
----------------------------------------
System.Xml
Assembly Version: 2.0.0.0
Win32 Version: 2.0.50727.42 (RTM.050727-4200)
CodeBase: file:///C:/WINDOWS/assembly/GAC_MSIL/System.Xml/2.0.0.0__b77a5c561934e089/System.Xml.dll
----------------------------------------
Microsoft.Office.Tools.Common
Assembly Version: 8.0.0.0
Win32 Version: 8.0.50727.444
CodeBase: file:///C:/WINDOWS/assembly/GAC_MSIL/Microsoft.Office.Tools.Common/8.0.0.0__b03f5f7f11d50a3a/Microsoft.Office.Tools.Common.dll
----------------------------------------
System.Windows.Forms
Assembly Version: 2.0.0.0
Win32 Version: 2.0.50727.42 (RTM.050727-4200)
CodeBase: file:///C:/WINDOWS/assembly/GAC_MSIL/System.Windows.Forms/2.0.0.0__b77a5c561934e089/System.Windows.Forms.dll
----------------------------------------
System.Drawing
Assembly Version: 2.0.0.0
Win32 Version: 2.0.50727.42 (RTM.050727-4200)
CodeBase: file:///C:/WINDOWS/assembly/GAC_MSIL/System.Drawing/2.0.0.0__b03f5f7f11d50a3a/System.Drawing.dll
----------------------------------------