Edited 9/3/2021 - Resolved the issue by upgrading this site from DNN 9.6.1 to 9.10.1 no apparent issues.

Hello Awesome Community:

I am working to upgrade several sites all of which started as DNN 7.x and upgraded through to DNN 8.0.3 about five years ago and left alone from thereafter. 

I have been able to successfully upgrade to 9.6.1 on one of the DNN instances as a proof of concept as there are 34 such sites. Each time I upgrade to DNN 9.8.1 or higher on my POC site, the Persona Bar disappears.

When accessing the url directly from F12 developer tools, I get the following error message.

I have searched high and low, what I don’t get is when I examine the web.config file, it is pointing to 5.2.3.0. I checked the versions of the assembly(s) in the bin folder and they match 5.2.3.0. I have upgraded through to DNN 9.10.0 from 9.6.1 and the issue persists. I have created a clean install of 9.10.0 and done a file comparison and moved the appropriate assemblies from bin to bin folder and still no dice. Upgrading higher and it does to point 5.2.7.0 vs 5.2.3 regardless I have also thought maybe there was another web.config for the personabar no dice. I have also downloaded the latest release version of DNN and can build and compile DNN in my home environment. At a loss on how to work through this and have applied much elbow grease. TIA all. 

An error has occurred.

Could not load file or assembly 'System.Web.Http, Version=5.2.7.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

System.IO.FileLoadException

 at System.ModuleHandle.ResolveType(RuntimeModule module, Int32 typeToken, IntPtr* typeInstArgs, Int32 typeInstCount, IntPtr* methodInstArgs, Int32 methodInstCount, ObjectHandleOnStack type) at System.ModuleHandle.ResolveTypeHandleInternal(RuntimeModule module, Int32 typeToken, RuntimeTypeHandle[] typeInstantiationContext, RuntimeTypeHandle[] methodInstantiationContext) at System.Reflection.RuntimeModule.ResolveType(Int32 metadataToken, Type[] genericTypeArguments, Type[] genericMethodArguments) at System.Reflection.CustomAttribute.FilterCustomAttributeRecord(CustomAttributeRecord caRecord, MetadataImport scope, Assembly& lastAptcaOkAssembly, RuntimeModule decoratedModule, MetadataToken decoratedToken, RuntimeType attributeFilterType, Boolean mustBeInheritable, Object[] attributes, IList derivedAttributes, RuntimeType& attributeType, IRuntimeMethodInfo& ctor, Boolean& ctorHasParameters, Boolean& isVarArg) at System.Reflection.CustomAttribute.GetCustomAttributes(RuntimeModule decoratedModule, Int32 decoratedMetadataToken, Int32 pcaCount, RuntimeType attributeFilterType, Boolean mustBeInheritable, IList derivedAttributes, Boolean isDecoratedTargetSecurityTransparent) at System.Reflection.CustomAttribute.GetCustomAttributes(RuntimeType type, RuntimeType caType, Boolean inherit) at System.Web.Http.Controllers.HttpControllerDescriptor.InvokeAttributesOnControllerType(HttpControllerDescriptor controllerDescriptor, Type type) at System.Web.Http.Controllers.HttpControllerDescriptor..ctor(HttpConfiguration configuration, String controllerName, Type controllerType) at DotNetNuke.Web.Api.DnnHttpControllerSelector.InitTypeCache() at System.Lazy`1.CreateValue() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Lazy`1.get_Value() at DotNetNuke.Web.Api.DnnHttpControllerSelector.SelectController(HttpRequestMessage request) at System.Web.Http.Tracing.Tracers.HttpControllerSelectorTracer.<>c__DisplayClass3.b__1() at System.Web.Http.Tracing.ITraceWriterExtensions.TraceBeginEnd(ITraceWriter traceWriter, HttpRequestMessage request, String category, TraceLevel level, String operatorName, String operationName, Action`1 beginTrace, Action execute, Action`1 endTrace, Action`1 errorTrace) at System.Web.Http.Tracing.Tracers.HttpControllerSelectorTracer.System.Web.Http.Dispatcher.IHttpControllerSelector.SelectController(HttpRequestMessage request) at System.Web.Http.Dispatcher.HttpControllerDispatcher.d__1.MoveNext()