"Catastrophic Failure" attempting to connect to SSRS Execution Service

I have a C# assembly that uses the SSRS report execution service (SQL 2008 R2 installation) to render reports. On my dev machine this code works fine; the requested report renders without issue.

However, when I attempt to deploy this assembly to another machine for testing (a SQL Server 2012 install) , this code:

ReportExecutionServiceexecutionService = newExecutionService.ReportExecutionService();

fails with the following error:

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)
   at System.Configuration.ClientConfigPaths..ctor(String exePath, Boolean includeUserConfig)
   at System.Configuration.ClientConfigPaths.GetPaths(String exePath, Boolean includeUserConfig)
   at System.Configuration.Internal.ConfigurationManagerInternal.System.Configuration.Internal.IConfigurationManagerInternal.get_ExeProductName()
   at System.Configuration.ApplicationSettingsBase.get_Initializer()
   at System.Configuration.ApplicationSettingsBase.CreateSetting(PropertyInfo propInfo)
   at System.Configuration.ApplicationSettingsBase.EnsureInitialized()
   at System.Configuration.ApplicationSettingsBase.get_Properties()
   at System.Configuration.SettingsBase.GetPropertyValueByName(String propertyName)
   at System.Configuration.SettingsBase.get_Item(String propertyName)
   at System.Configuration.ApplicationSettingsBase.GetPropertyValue(String propertyName)
   at System.Configuration.ApplicationSettingsBase.get_Item(String propertyName)

Interestingly, if I attempt to call it again immediately, I get the following error instead:

System.Configuration.SettingsPropertyNotFoundException: The settings property 'MyAssembly_ExecutionService_ReportExecutionService' was not found.

I've tried the following things:

1. checked the settings.settings file, the app.config, and the web reference file and confirmed that the setting is referred to as MyAssembly_ExecutionService_ReportExecutionService
2. Dropped and recreated the web service reference, changing the name to something else (MyAssembly2): the references are all updated but the error recurs as unable to find 'MyAssembly2_ExecutionService_ReportExecutionService'
3. Installed VS on the other machine and rebuilt the solution from scratch (same errors)
4. Ensured the execution service is running: I can access it through the browser and verified it is running through the SSRS config manager
5. restarted the service
6. rebooted the server
7. Looked online for issues related to SQL 2012 (though hopefully #3 would have addressed any such issues) and didn't find anything.

 There is nothing showing up in logging for SQL or in the Event Viewer. I suspect that the first error is really the issue and the SettingsPropertyNotFound exception is just a symptom, but I am completely out of ideas as to why at this point.

Any help would be appreciated.