title: CannotCreateCustomizationDomainException: Customization could not be loaded because the application domain could not be created
body: <p>I'm trying to run an Excel 2007 VSTO 3.0 addin we've created.  However since installing the ION Trading MarketView Excel Plug-in our add-in no longer seems to load properly and fails with the following error:</p>
  <blockquote>
  <p>Microsoft.VisualStudio.Tools.Applications.Runtime.CannotCreateCustomizationDomainException: Customization could not be loaded because the application domain could not be created. ---&gt; System.IO.FileLoadException: Loading this assembly would produce a different grant set from other instances. (Exception from HRESULT: 0x80131401)</p>
  <p>at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean&amp; canBeCached, RuntimeMethodHandle&amp; ctor, Boolean&amp; bNeedSecurityCheck)
  at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean fillCache)
  at System.RuntimeType.CreateInstanceImpl(Boolean publicOnly, Boolean skipVisibilityChecks, Boolean fillCache)
  at System.Activator.CreateInstance(Type type, Boolean nonPublic)
  at System.RuntimeType.CreateInstanceImpl(BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes)
  at System.Activator.CreateInstance(Type type, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes)
  at System.Activator.CreateInstance(String assemblyName, String typeName, Boolean ignoreCase, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes, Evidence securityInfo, StackCrawlMark&amp; stackMark)
  at System.Activator.CreateInstance(String assemblyName, String typeName)
  at System.AppDomain.CreateInstance(String assemblyName, String typeName)
  at System.AppDomain.CreateInstanceAndUnwrap(String assemblyName, String typeName)
  at System.AppDomain.CreateInstanceAndUnwrap(String assemblyName, String typeName)
  at Microsoft.VisualStudio.Tools.Office.Runtime.DomainCreator.LoadMafPipeline(AppDomain newDomain, IntPtr hostServiceProvider, AddInInformation info, EntryPoints requestedEntryPoints, OfficeApp officeApplication, OfficeVersion officeVersion, IntPtr&amp; executor)
  at Microsoft.VisualStudio.Tools.Office.Runtime.DomainCreator.CreateCustomizationDomainInternal(String solutionLocation, String manifestName, String documentName, Boolean showUIDuringDeployment, IntPtr hostServiceProvider, IntPtr&amp; executor)
  --- End of inner exception stack trace ---</p>
  </blockquote>
  <p>Does anyone have any idea what could be causing this?  Any pointers for how I could investigate further?</p>
  <p>Thanks,
  Tom</p>