System.InvalidOperationException when calling TeamFoundationServer.GetService()

After working fine all day, calling this:
Client.WorkItemStore store = server.GetService(typeof(Client.WorkItemStore))as Client.WorkItemStore;

causes the following error:

Please Advise,

Michael S. Scherotter
Business Solutions Architect
Mindjet Corporation

Error Message:

MindManager.exe Error: 0 : System.InvalidOperationException: Unable to generate a temporary class (result=1).

error CS0103: The name 'WriteElementSt?ingRaw' does not exist in the current context

Stack Trace:

at System.Xml.Serialization.Compiler.Compile(Assembly parent, String ns, CompilerParameters parameters, Evidence evidence)

at System.Xml.Serialization.TempAssembly.GenerateAssembly(XmlMapping[] xmlMappings, Type[] types, String defaultNamespace, Evidence evidence, CompilerParameters parameters, Assembly assembly, Hashtable assemblies)

at System.Xml.Serialization.TempAssembly..ctor(XmlMapping[] xmlMappings, Type[] types, String defaultNamespace, String location, Evidence evidence)

at System.Xml.Serialization.XmlSerializer.FromMappings(XmlMapping[] mappings, Type type)

at System.Web.Services.Protocols.SoapClientType..ctor(Type type)

at System.Web.Services.Protocols.SoapHttpClientProtocol..ctor()

at Microsoft.TeamFoundation.Client.TeamFoundationSoapProxy..ctor()

at Microsoft.TeamFoundation.WorkItemTracking.Proxy.ClientServiceProxy..ctor()

at Microsoft.TeamFoundation.WorkItemTracking.Proxy.ClientService.GetProxy(String requestId)

at Microsoft.TeamFoundation.WorkItemTracking.Proxy.ClientService.GetMetadataEx2(String requestId, Boolean useMaster, MetadataTableHaveEntry[] metadataHave, String& dbStamp, IMetadataRowSets& metadata, Int32& locale, Int32& comparisonStyle, Int32& displayMode)

at CProdStudioBackendChannel.GetMetadata(CProdStudioBackendChannel* , tagVARIANT* pvarLocale, tagVARIANT* pvarComparisonStyle, PsUserDisplayModeEnum* pDisplayMode, Boolean* pfUseSIDSecurity, Int32 fNoFire, Int32 fByPassFireOnThis)