Failure decoding embedded permission set object After .Net service pack install

[David Hodges]

After installing the service packs from Framework 1.0 and 1.1 on my
W2k web server I get the above error on all applications.
I am at my wits end and finding nothing on Google that helps.

Here is the complete error:

Security Exception
Description: The application attempted to perform an operation not
allowed by the security policy. To grant this application the required
permission please contact your system administrator or change the
application's trust level in the configuration file.

Exception Details: System.Security.SecurityException: Failure decoding
embedded permission set object.

Source Error:

An unhandled exception was generated during the execution of the
current web request. Information regarding the origin and location of
the exception can be identified using the exception stack trace below.

Stack Trace:
[SecurityException: Failure decoding embedded permission set object.]
System.RuntimeType.CreateInstanceImpl(Boolean publicOnly) +0
System.Activator.CreateInstance(Type type, Boolean nonPublic) +66
System.RuntimeType.CreateInstanceImpl(BindingFlags bindingAttr,
Binder binder, Object[] args, CultureInfo culture, Object[]
activationAttributes) +277
System.Activator.CreateInstance(Type type, BindingFlags
bindingAttr, Binder binder, Object[] args, CultureInfo culture,
Object[] activationAttributes) +109

System.Web.Configuration.HttpCapabilitiesEvaluator .Evaluate(HttpRequest
request) +719

System.Web.Configuration.HttpCapabilitiesBase.GetC onfigCapabilities(String
configKey, HttpRequest request) +43
System.Web.HttpRequest.get_Browser() +22
System.Web.UI.WebControls.ValidationSummary.OnPreR ender(EventArgs
e) +96
System.Web.UI.Control.PreRenderRecursiveInternal() +62
System.Web.UI.Control.PreRenderRecursiveInternal() +125
System.Web.UI.Control.PreRenderRecursiveInternal() +125
System.Web.UI.Control.PreRenderRecursiveInternal() +125
System.Web.UI.Control.PreRenderRecursiveInternal() +125
System.Web.UI.Page.ProcessRequestMain() +2095
System.Web.UI.Page.ProcessRequest() +118
System.Web.UI.Page.ProcessRequest(HttpContext context) +18
System.Web.CallHandlerExecutionStep.Execute() +179
System.Web.HttpApplication.ExecuteStep(IExecutionS tep step,
Boolean& completedSynchronously) +87
Any ideas?
Thanks,
David