ODP.NET IIS 7.5 WEB API error

Question

I have just migrated my ASP.NET 4.0 C# website from IIS 6 to IIS 7.5 I installed via nuget Oracle Managed and ODP.NET Managed packages to my project. I'm having this error when trying to access my ASP.NET WEB API. How do I troubleshoot this? Thanks

<Error>
<Message>An error has occurred.</Message>
<ExceptionMessage>
The 'ObjectContent`1' type failed to serialize the response body for content type 'application/xml; charset=utf-8'.
</ExceptionMessage>
<ExceptionType>System.InvalidOperationException</ExceptionType>
<StackTrace/>
<InnerException>
<Message>An error has occurred.</Message>
<ExceptionMessage>
Exception has been thrown by the target of an invocation.
</ExceptionMessage>
<ExceptionType>System.Reflection.TargetInvocationException</ExceptionType>
<StackTrace>
at System.RuntimeFieldHandle.GetValue(RtFieldInfo field, Object instance, RuntimeType fieldType, RuntimeType declaringType, Boolean& domainInitialized) at System.Reflection.RtFieldInfo.InternalGetValue(Object obj, Boolean doVisibilityCheck, Boolean doCheckConsistency) at System.Reflection.RtFieldInfo.GetValue(Object obj) at System.Data.Common.DbProviderFactories.GetFactory(DataRow providerRow) at System.Data.Common.DbProviderFactories.GetFactory(String providerInvariantName) at System.Data.EntityClient.EntityConnection.GetFactory(String providerString) at System.Data.EntityClient.EntityConnection.ChangeConnectionString(String newConnectionString) at System.Data.EntityClient.EntityConnection..ctor(String connectionString) at System.Data.Entity.Internal.LazyInternalConnection.InitializeFromConnectionStringSetting(ConnectionStringSettings appConfigConnection) at System.Data.Entity.Internal.LazyInternalConnection.TryInitializeFromAppConfig(String name, AppConfig config) at System.Data.Entity.Internal.LazyInternalConnection.Initialize() at System.Data.Entity.Internal.LazyInternalConnection.CreateObjectContextFromConnectionModel() at System.Data.Entity.Internal.LazyInternalContext.InitializeContext() at System.Data.Entity.Internal.InternalContext.GetEntitySetAndBaseTypeForType(Type entityType) at System.Data.Entity.Internal.Linq.InternalSet`1.Initialize() at System.Data.Entity.Internal.Linq.InternalSet`1.GetEnumerator() at System.Data.Entity.Infrastructure.DbQuery`1.System.Collections.Generic.IEnumerable<TResult>.GetEnumerator() at WriteArrayOfADDRESSTYPEToXml(XmlWriterDelegator , Object , XmlObjectSerializerWriteContext , CollectionDataContract ) at System.Runtime.Serialization.CollectionDataContract.WriteXmlValue(XmlWriterDelegator xmlWriter, Object obj, XmlObjectSerializerWriteContext context) at System.Runtime.Serialization.XmlObjectSerializerWriteContext.WriteDataContractValue(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, RuntimeTypeHandle declaredTypeHandle) at System.Runtime.Serialization.XmlObjectSerializerWriteContext.SerializeAndVerifyType(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, Boolean verifyKnownType, RuntimeTypeHandle declaredTypeHandle, Type declaredType) at System.Runtime.Serialization.XmlObjectSerializerWriteContext.SerializeWithXsiTypeAtTopLevel(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, RuntimeTypeHandle originalDeclaredTypeHandle, Type graphType) at System.Runtime.Serialization.DataContractSerializer.InternalWriteObjectContent(XmlWriterDelegator writer, Object graph, DataContractResolver dataContractResolver) at System.Runtime.Serialization.DataContractSerializer.InternalWriteObject(XmlWriterDelegator writer, Object graph, DataContractResolver dataContractResolver) at System.Runtime.Serialization.XmlObjectSerializer.WriteObjectHandleExceptions(XmlWriterDelegator writer, Object graph, DataContractResolver dataContractResolver) at System.Runtime.Serialization.DataContractSerializer.WriteObject(XmlWriter writer, Object graph) at System.Net.Http.Formatting.XmlMediaTypeFormatter.<>c__DisplayClass7.<WriteToStreamAsync>b__6() at System.Threading.Tasks.TaskHelpers.RunSynchronously(Action action, CancellationToken token)
</StackTrace>
<InnerException>
<Message>An error has occurred.</Message>
<ExceptionMessage>
The type initializer for 'Oracle.DataAccess.Client.OracleClientFactory' threw an exception.
</ExceptionMessage>
<ExceptionType>System.TypeInitializationException</ExceptionType>
<StackTrace/>
<InnerException>
<Message>An error has occurred.</Message>
<ExceptionMessage>
The provider is not compatible with the version of Oracle client
</ExceptionMessage>
<ExceptionType>Oracle.DataAccess.Client.OracleException</ExceptionType>
<StackTrace>
at Oracle.DataAccess.Client.OracleInit.Initialize() at Oracle.DataAccess.Client.OracleClientFactory..cctor()
</StackTrace>
</InnerException>
</InnerException>
</InnerException>
</Error>

Answer 1

Contrary to the problem statement, it appears that the application is using the unmanaged client (namespace Oracle.DataAccess.Client) instead of the managed client (namespace Oracle.ManagedDataAccess.Client) and that it's incompatible with the Oracle Client installed on the machine.