I'm use Enterprise library Validation block intergrated with WCF. It reports System.Runtime.InteropServices.COMException (0x8000FFFF): Catastrophic failure (Exception from HRESULT: 0x8000FFFF (E_UNEXPECTED)) when I impersonate some other user with WIN32 API LogonUser and WindowsIdentity.Impersonate. It seems there is something wrong when to get security evidence on loading configuration. If I remove the coding of impersonation, it works without any errors. These are the part of the exception stack trace, hope you give some helpers. thanks.

System.Runtime.InteropServices.COMException (0x8000FFFF): Catastrophic failure (Exception from HRESULT: 0x8000FFFF (E_UNEXPECTED))
   at System.Security.Policy.PEFileEvidenceFactory.GetLocationEvidence(SafePEFileHandle peFile, SecurityZone& zone, StringHandleOnStack retUrl)
   at System.Security.Policy.PEFileEvidenceFactory.GenerateLocationEvidence()
   at System.Security.Policy.PEFileEvidenceFactory.GenerateEvidence(Type evidenceType)
   at System.Security.Policy.AssemblyEvidenceFactory.GenerateEvidence(Type evidenceType)
   at System.Security.Policy.Evidence.GenerateHostEvidence(Type type, Boolean hostCanGenerate)
   at System.Security.Policy.Evidence.GetHostEvidenceNoLock(Type type)
   at System.Security.Policy.Evidence.GetHostEvidence(Type type, Boolean markDelayEvaluatedEvidenceUsed)
   at System.Security.Policy.AppDomainEvidenceFactory.GenerateEvidence(Type evidenceType)
   at System.Security.Policy.Evidence.GenerateHostEvidence(Type type, Boolean hostCanGenerate)
   at System.Security.Policy.Evidence.GetHostEvidenceNoLock(Type type)
   at System.Security.Policy.Evidence.RawEvidenceEnumerator.MoveNext()
   at System.Security.Policy.Evidence.EvidenceEnumerator.MoveNext()
   at System.Configuration.ClientConfigPaths.GetEvidenceInfo(AppDomain appDomain, String exePath, String& typeName)
   at System.Configuration.ClientConfigPaths.GetTypeAndHashSuffix(AppDomain appDomain, String exePath)
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