Loading this assembly would produce a different grant set from other instances

After installing .NET 3.5 sp1, all the MOSS web applications were working fine except for one. The following error was showing up:

Stack trace:
at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandle& ctor, Boolean& 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)
at System.Web.Configuration.Common.ModulesEntry.Create()
at System.Web.Configuration.HttpModulesSection.CreateModules()
at System.Web.HttpApplication.InitInternal(HttpContext context, HttpApplicationState state, MethodInfo[] handlers)
at System.Web.HttpApplicationFactory.GetNormalApplicationInstance(HttpContext context) at System.Web.HttpApplicationFactory.GetApplicationInstance(HttpContext context)
at System.Web.HttpRuntime.ProcessRequestInternal(HttpWorkerRequest wr)

Fix:
Just restart the application pool account associated with the erroring application and you be all set.