I am developing a simple Outlook 2003 add-in using VSTO 2008. Everything works fine on development environment. But when I try to install the addin it gives following load error. I think there is some security related issue. Please help me in resolving this issue. Could not load file or assembly 'OutlookAddIn, 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 'OutlookAddIn, 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: 'OutlookAddIn, 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: 2.0.50727.3603 (GDR.050727-3600) 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: 8.0.50727.940 CodeBase: file:///C:/WINDOWS/assembly/GAC_MSIL/Microsoft.VisualStudio.Tools.Applications.Runtime/8.0.0.0__b03f5f7f11d50a3a/Microsoft.VisualStudio.Tools.Applications.Runtime.dll ---------------------------------------- Microsoft.Office.Tools.Common Assembly Version: 8.0.0.0 Win32 Version: 8.0.50727.940 CodeBase: file:///C:/WINDOWS/assembly/GAC_MSIL/Microsoft.Office.Tools.Common/8.0.0.0__b03f5f7f11d50a3a/Microsoft.Office.Tools.Common.dll ---------------------------------------- System Assembly Version: 2.0.0.0 Win32 Version: 2.0.50727.3053 (netfxsp.050727-3000) CodeBase: file:///C:/WINDOWS/assembly/GAC_MSIL/System/2.0.0.0__b77a5c561934e089/System.dll ---------------------------------------- System.Windows.Forms Assembly Version: 2.0.0.0 Win32 Version: 2.0.50727.3053 (netfxsp.050727-3000) CodeBase: file:///C:/WINDOWS/assembly/GAC_MSIL/System.Windows.Forms/2.0.0.0__b77a5c561934e089/System.Windows.Forms.dll ----------------------------------------