Upgrading from 3.4 to 3.9

I'm experiencing issues...specifically the generic error page.
http://luvmineralcosmetics.net/errorpage.htm?aspxerrorpath=/

Here are the steps I've completed so far.
Backup the database and files.
Run upgrade script for 3.5
Delete all files.
Upload new 3.5 files.
Restore installated plugins.txt and settings.txt
Uploaded Content/images/
uploaded themes/dresscode/

Error results.

Any ideas/suggestions/help? Would be very much appreciated.

I have changed the web.config file to the following:
<customErrors defaultRedirect="errorpage.htm" mode="Off">

Which is revealing (I think) an error in the theme code?

Error is in the Views/Widget/WidgetsByZone.cshtml file according to the error page. Sadly, my skills with nop commerece and .net are nil, so again, any help would be so greatly appreciated!

I've proceeded to upgrade the database step-wise to 3.9.
Still receiving errors.
http://luvmineralcosmetics.net/en/

It appears the errors are coming from the plugin manager. I've made certain to update installedPlugins.txt per the upgrade instructions and removed the old plugin folders.



[FileLoadException: Could not load file or assembly 'Newtonsoft.Json, Version=6.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)]

[FileLoadException: Could not load file or assembly 'Newtonsoft.Json, Version=9.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)]
   System.Reflection.RuntimeAssembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +0
   System.Reflection.RuntimeAssembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +36
   System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, RuntimeAssembly reqAssembly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +152
   System.Reflection.Assembly.Load(AssemblyName assemblyRef) +36
   Nop.Core.Plugins.PluginManager.PerformFileDeploy(FileInfo plug) +169
   Nop.Core.Plugins.PluginManager.Initialize() +1327

[Exception: Plugin 'Credit Card'. Could not load file or assembly 'Newtonsoft.Json, Version=9.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)]
   Nop.Core.Plugins.PluginManager.Initialize() +2029

[Exception: Plugin 'Credit Card'. Could not load file or assembly 'Newtonsoft.Json, Version=9.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
Could not load file or assembly 'Newtonsoft.Json, Version=9.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
Could not load file or assembly 'Newtonsoft.Json, Version=6.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
]
   Nop.Core.Plugins.PluginManager.Initialize() +2437

[InvalidOperationException: The pre-application start initialization method Initialize on type Nop.Core.Plugins.PluginManager threw an exception with the following error message: Plugin 'Credit Card'. Could not load file or assembly 'Newtonsoft.Json, Version=9.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
Could not load file or assembly 'Newtonsoft.Json, Version=9.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
Could not load file or assembly 'Newtonsoft.Json, Version=6.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
.]
   System.Web.Compilation.BuildManager.InvokePreStartInitMethodsCore(ICollection`1 methods, Func`1 setHostingEnvironmentCultures) +613
   System.Web.Compilation.BuildManager.InvokePreStartInitMethods(ICollection`1 methods) +141
   System.Web.Compilation.BuildManager.CallPreStartInitMethods(String preStartInitListPath, Boolean& isRefAssemblyLoaded) +102
   System.Web.Compilation.BuildManager.ExecutePreAppStart() +157
   System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters, PolicyLevel policyLevel, Exception appDomainCreationException) +531

[HttpException (0x80004005): The pre-application start initialization method Initialize on type Nop.Core.Plugins.PluginManager threw an exception with the following error message: Plugin 'Credit Card'. Could not load file or assembly 'Newtonsoft.Json, Version=9.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
Could not load file or assembly 'Newtonsoft.Json, Version=9.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
Could not load file or assembly 'Newtonsoft.Json, Version=6.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
.]
   System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +9946024
   System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +90
   System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +261

Ok. Two issues. The theme was old and useless. I had to remove it.
I also had to reupload the Newtonsoft.json.dll to the bin folder.

These two things got the site up and running smoothly again.